Reclaiming the Biology of Self-Control

AMONG THE THIRTY-FIVE thousand people who ran the New York City Marathon in November of 2006 were sixteen former drug addicts, a number of whom joked openly that they’d spent most of their lives “running from the cops.” When they crossed the finish line, the distance they had come was far greater than 26.2 miles. Many of them had been imprisoned, homeless, or otherwise destitute when they checked themselves into Odyssey House, a rehabilitation program in New York that treats about eight hundred residents at half a dozen locations throughout the city.

These are the rare, worst-case examples of what can happen to people who completely lose control of their behavior. And while the lives of those addicted to hard drugs such as crack or heroin or crystal meth look drastically different than the lives of those who use or abuse drugs without being hooked, the same principles apply to their brains. Which is to say that the lessons of Odyssey House apply to anyone who struggles with self-control, including those who think of themselves as having addictive personalities. Scientists are now characterizing behavior such as gambling, compulsive shopping, and even overeating in the same biological terms they use to explain substance abuse. The common denominator is an out-of-control reward system, which some people are born with and some people develop.

Odyssey House has been around since the late 1960s, offering services from counseling to job training, elder care to family reconciliation. In the spring of 2000, an employee named John Tavolacci started taking residents running in Central Park, with the goal of training for a 5K charity run held each fall. “We run in groups with them and talk about what goes into running — the discipline, the structure, the teamwork,” says Tavolacci, who is now Odyssey House’s chief operating officer. “Addicts usually isolate themselves, but here they motivate one another, and they see what it means to set goals and accomplish them.”

Many of his charges start out walking, and their first challenge is to follow the one rule Tavolacci imposes: no smoking. Then they build up to running the 1.58 miles around the Central Park Reservoir. About a hundred or so residents participate in the exercise program, which is called “Run for Your Life,” and those who become serious runners stay in treatment about twice as long as the nonactive residents. “It sounds obvious,” Tavolacci says, “But the only thing that we know about treatment is the longer a person stays in, the more likely they are to succeed.”

Odyssey House has always used a holistic approach to treatment and emphasizes the importance of community. This is crucial, according to Odyssey House director Peter Provet, because addiction is such an all-encompassing disorder, cutting into every aspect of life, from family to mood to work. “The drug, for the addict, becomes everything,” Provet says. Take it away and suddenly there is an “empty vessel” at the core of the body and mind.

“What better way to start filling the vessel than exercise,” Provet suggests. “I strongly believe that exercise can serve as an antidote and as a type of inoculation against addiction,” he says. “As an antidote, you’re giving the individual an avenue of life experience that most have not had — the goals of exercise, the feeling of exercise, the challenge of exercise, the pleasure and the pain, the accomplishment, the physical well-being, the self-esteem. All that exercise gives us, you’re now presenting to the addict as a very compelling option.”

Inoculation ranks as equally important, given that most addicts fight a protracted, sometimes lifelong, battle with relapse. And Provet sees exercise as the best form of inoculation. “Exercise is directly antithetical to drug-addictive behavior. Because you need lung strength, muscle strength, mental acuity to engage in physical exercise — lots of things that drugs deprive you of. If you’re not eating, not caring about your body, letting it waste away, having your mind distorted by being constantly intoxicated, you can’t be a serious exerciser. You can’t do it.

Neurobiology is just catching up with what twenty years of experience have taught Provet. The way he describes exercise’s effect on the addict mirrors what I discussed in chapter 5, about depression. As a treatment, exercise works from the top down in the brain, forcing addicts to adapt to a new stimulus and thereby allowing them to learn and appreciate alternative and healthy scenarios. It’s activity-dependent training, and while it may not provide the immediate rush of a snort of cocaine, it instills a more diffuse sense of well-being that, over time, will become a craving in its own right. The inoculation works from the bottom up, physically blunting the urge to act by engaging the more primitive elements of the brain. Exercise builds synaptic detours around the well-worn connections automatically looking for the next fix.

“Not everyone is going to become a marathon runner, but more and more we’re going from addict to athlete,” says Provet. “Is it for everybody? Probably not. Is it for most people? Probably yes.”


As with so many discoveries about how the brain works, scientists stumbled on the first clues about addiction by accident. In 1954 psychologist James Olds and a graduate student named Peter Milner, at McGill University in Montreal, were studying behavior by inserting electrodes into the brains of live rats. They wanted to pinpoint an area related to learning, but in one of the animals, the electrode ended up in the wrong spot. The result was even more interesting than what they were looking for: The rat kept returning to the corner of its cage where it received its first jolt. To the researchers’ amazement, they found they could steer the rodent like a remote-control toy by doling out bursts of electricity. The next day, the rat sought out the same comer. Clearly, the rat wanted the stimulation, so much so that it would ignore food placed in one corner in order to receive the shock in another.

In the most famous of their experiments, Olds and Milner rigged up a lever so the rat could administer its own brain stimulation. After discovering that pressing the lever delivered a jolt, it pressed it about once every five seconds until the juice was switched off. Then the rat pawed at the lever a few times with no result and promptly fell asleep.

The brain area that Olds and Milner hit with that electrode is closely related to the nucleus accumbens, or reward center, and it has been the focus of addiction research ever since. It’s a critical node of the attention system, as I described in the last chapter, and it’s also important in addiction. The reward center provides the necessary motivation for the brain to learn behavior that brings us things we like or want or need. All the things people become addicted to — alcohol, caffeine, nicotine, drugs, sex, carbohydrates, gambling, playing video games, shopping, living on the edge — boost the dopamine in the nucleus accumbens. Regardless of the varying psychological effects different drugs have on the mind, they all boost dopamine in the reward center. As an illustration of the power of drugs, consider that while sex increases dopamine levels 50 to 100 percent, cocaine sends dopamine skyrocketing 300 to 800 percent beyond normal levels.

The nucleus accumbens used to be known as the pleasure center, fueling the notion that addicts are essentially looking for a good time. And while pleasure is certainly an initial factor in enticing people to try a drug or their luck at a gaming table, it’s not quite right to think of addicts purely as hedonists. Nobody enjoys being addicted. Indeed, by studying how dopamine works as the key messenger in the reward system, scientists have drawn a distinction between liking something and wanting it. “Liking refers to the actual experience of pleasure, versus the motivational state, which is the willingness to work for rewards,” says Terry Robinson, a behavioral neuroscientist at the University of Michigan. “Dopamine is involved in this wanting, but it’s not involved in liking.”

The reward center is where ADHD and addiction overlap, which explains why both problems undermine motivation, self-control, and memory. It is no coincidence that about half of those with ADHD also struggle with substance abuse of some kind. The implications have changed the way scientists describe addiction.

The pivotal issues seem to be salience and motivation rather than pleasure. In this context, salience means something that stands out against the landscape of life, predominating over all other stimuli. Cues for both pleasure and pain send dopamine coursing through the nucleus accumbens to attract our attention so we can take action to survive. For the developing substance abuser, the overload of dopamine has tricked the brain into thinking that paying attention to the drug is a matter of life or death. “Drugs are tapping into the very core systems that have evolved to mediate survival,” says Robinson. “They activate the system in ways it was never meant to be activated.”

The National Institute on Drug Abuse now defines addiction as a compulsion that persists in spite of negative health and social consequences. Plenty of people use and abuse drugs, but only relatively few become addicts. Why? While dopamine in the reward center creates the initial interest in a drug or behavior and provides the motivation to get it, what makes addiction such a stubborn problem is the structural changes it causes in the brain. Scientists now consider addiction a chronic disease because it wires in a memory that triggers reflexive behavior. The same changes occur regardless of whether the addiction is to drugs or gambling or eating.

Once the reward has the brain’s attention, the prefrontal cortex instructs the hippocampus to remember the scenario and sensation in vivid detail. If it’s greasy food that you can’t resist, the brain links the aroma of Kentucky Fried Chicken to Colonel Sanders’s beard and that red and white bucket. Those cues take on salience and get linked together into a web of associations. Each time you drive up to KFC, the synaptic connections linking everything together get stronger and pick up new cues. This is how habits are formed.

Typically, when we learn something, the connections stabilize and the levels of dopamine tail off over time. With addiction, especially drug addiction, dopamine floods the system with each drug use, reinforcing the memory and pushing other stimuli further into the background. Animal studies show that drugs such as cocaine and amphetamine make the dendrites in the nucleus accumbens bloom, thus increasing their synaptic connections. The changes can remain months and maybe even years after the drugs are stopped, which is why it’s so easy to relapse. One way to look at addiction is that the brain has learned something too well. These adaptations lead to a vicious cycle in which the basal ganglia goes on autopilot whenever you smell fried chicken, and the prefrontal cortex can’t override your actions even though you may know better.

One of the responsibilities of the prefrontal cortex is to assess risk versus reward and to decide whether to inhibit behavior that may cause harm. With addicts, it’s not so much that they make bad choices as that they fail to inhibit behavior that has become reflexive. We know from studies in animals and humans that cocaine, for one, damages nerve cells in the prefrontal cortex and even reduces gray matter. And in recent years, imaging studies have shown that the prefrontal cortex doesn’t fully develop until we are well into our twenties, which could explain why most people who experiment with drugs and get hooked do so as teenagers or during early adulthood, when their inhibition hasn’t fully developed. “They end up with a hypersensitive system that wants drugs, and they make very bad decisions,” says Robinson. “It’s the worst of both possible worlds.”


There’s nothing like appearing before a judge to hasten the development of a teenager’s inhibition. A patient of mine named Rusty might have ended up a drug addict, but the prospect of three years in jail scared him into cleaning up his act, and the exercise routine he developed in the process is why he’s still on the right track today.

I began treating Rusty the summer after his sophomore year in high school, a few months after he was hospitalized for attempting suicide. Feeling lonely and outcast, he had washed down a stash of pills with a pint of peach schnapps. He had good test scores — along with bad grades and a history of tantrums — but no friends at all. It was clear to me that he suffered from an attention deficit, combined with fairly severe symptoms of what I call social dyslexia, meaning he didn’t know how to talk to people or be relaxed and flexible in conversation. Rusty’s strategy to be cool and make friends was to dress in all black and sell marijuana that he grew himself.

I put him on a long-acting stimulant — a drug he couldn’t abuse — for ADHD, and he picked up his grades a little and did very well on the SATs the spring of his junior year. Still, whenever he felt bored or at a loss, he would take anything he could get his hands on, from cocaine to cough syrup. Home alone one afternoon his senior year, he had a panic attack from too much cocaine and called 911. An ambulance came right away — along with the police, who found drugs in his room. He was arrested for possession and intent to distribute and spent the night in jail.

A court date was set for four months down the road, and his lawyer and I worked out a treatment plan — each week he had to take two drug tests and attend a meeting at Alcoholics Anonymous and one at Narcotics Anonymous. He knew he had to stay clean at least until his court appearance, but he started to crave cocaine. His lawyer told him he’d probably get the maximum sentence of three years in jail, and he desperately wanted help. Dealing with his cravings was our first order of business, and I told Rusty that exercise could have a huge impact. He didn’t like running or sports, and aside from a stint playing soccer as a child, he was essentially physically inert. I had just returned from my first visit to Naperville, and perhaps because of the way he dressed, I thought of a goth girl named Rachel who had really transformed herself by playing Dance Dance Revolution (DDR), the interactive video game in which the player controls the action on screen by dancing on a mat that’s connected to the television. The footwork involved is exhausting even to watch, like the tire drill football players practice, except that the game gets faster and faster at each level.

Rusty agreed to try it, and although he felt clumsy at first, he started to enjoy it. Almost immediately, he said, it blunted his cravings. With nothing much to do that summer except worry about whether he’d be going to jail, he used the game to fill his time and to medicate himself. Guarding against boredom is critical because idle time is dangerous for someone fighting a drug habit.

Rusty got to the point where he was playing DDR several hours in the morning and at night, every day. I saw that his energy level and his optimism picked up. I wrote a letter to the judge, and Rusty was put on probation rather than given jail time, on the condition that he would continue drug testing, Narcotics Anonymous, and counseling at college. He took his DDR setup with him and continued doing it every day for a while. Then he joined an intramural soccer team and started going to the gym.

Exercise was a conduit for shifting Rusty’s focus to a more productive life. I see exercise as a way of offsetting the feeling of hopelessness and uselessness that a lot of drug users have, and that certainly was a factor with Rusty. The routine and the physical activity gets the brain engaged and the mind moving in a direction other than toward the drug, reprogramming the basal ganglia to wire in an alternative reflexive behavior. Many people retreat to the couch and give up, but being in motion fosters the feeling that you can accomplish something.

A doctor named Gene-Jack Wang, one of the country’s foremost addiction researchers and chairman of the medical department at Brookhaven National Laboratory, talks about movement in philosophical terms. “In the Chinese language, a subject is an animal, and an object is a vegetable,” he says. “You cannot ask a vegetable to jump from here to there. If you don’t move, you are not an animal anymore — you become a vegetable!”

Certainly this is a factor with the marathoners of Odyssey House. But even with a milder case such as Rusty’s, doing DDR chased the bleakness out of his view of his future. And while most experiences will pale in comparison to the high of snorting cocaine, the possibility of a rich life can help keep that memory in perspective.

Rusty is now in his sophomore year of college, making good grades, and dating a girl who is also committed to staying sober. He’s taken a leadership role in his dorm, and he’s gotten into rock climbing as well as playing soccer. He even started scuba diving, a family activity that he’d avoided in the past. After a recent diving vacation, he told me that he is constantly amazed to see how rich and colorful natural life can be.


What Rusty finally sees — that he can find pleasure without drugs — is vital to resisting the urge. When you talk to hard-core addicts, you often hear that they feel numb to most things. Naturally satisfying forms of stimulation such as love, food, and social interaction are a bland backdrop to the vivid experience of the drug. The normal course of life doesn’t do it — they can’t feel it.

Some people are simply born this way. A groundbreaking study in 1990 revealed, for instance, that a lot of alcoholics have a gene variation (the D2R2 allele) that robs their reward center of dopamine receptors, lowering levels of the neurotransmitter. Presence of the D2R2 allele doesn’t guarantee you’ll end up as an addict, but it’s more likely. While 25 percent of the general population has the variation, in one study researchers found it in 70 percent of alcoholics who had cirrhosis — presumably the most addicted, since they continued drinking in the face of life-threatening liver damage. In a subsequent study of cocaine addicts, half had the D2R2 allele, and 80 percent of those who also abused other drugs had it. Results tell a similar story with gamblers and the morbidly obese: about half display the gene variation, but when we factor in other addictive behavior, it’s more like 80 percent. Researchers named this problem reward-deficiency syndrome, and the media declared that scientists had found the “alcoholic gene.”

Unfortunately, it’s not that simple. Without question, if the reward center isn’t receiving enough input, you’re genetically predisposed to be constantly craving, relentlessly searching for a way to compensate for the deficit. Reward deficiency also undermines the attention and stress systems: when dopamine is out of balance, the amygdala gets involved because it thinks survival is at risk, and that intensifies the pursuit of bringing the brain to equilibrium. This relates back to why so many people with ADHD are seen as “stress junkies” — cortisol quickly boosts dopamine to improve attention. You can see how this nagging feeling — people describe it as a hollowness inside — could leave a person vulnerable to addictive behavior, from taking drugs to gorging on chocolate to playing video games forty hours a week.

But just because you have reward-deficiency syndrome doesn’t mean you’re destined for Odyssey House. There are hundreds, if not thousands, of factors that influence addiction, and the drive to find something new and exciting can just as easily turn people into bold explorers, iconoclastic artists, or maverick entrepreneurs or send them down any number of paths where pushing conventional boundaries and seeing the world differently are highly valued commodities.

Not surprisingly, athletes in high-risk sports like skydiving display less inhibition and more thrill-seeking behavior than, say, rowers. A recent study from Holland also showed that, like hard-core addicts, many skydivers don’t experience pleasure from typical daily life. Both skydivers and addicts have a higher-than-normal threshold for excitement, but is that the cause or the result of the dopamine-boosting behavior? Other research shows that drugs such as cocaine damage D2 receptors, the slots the neurotransmitter plugs into to signal salience. If you continually subject your brain to an overload of dopamine, the number of receptors will dwindle. So regardless of what your brain looked like when you were born, the more drugs you take, the more drugs you’ll need to feel the same rush. The same is true of people of people who overeat: “You need more, more, more to make you feel good,” says Brookhaven’s Gene-Jack Wang.


A study in London in 2004 showed that even ten minutes of exercise could blunt an alcoholic’s craving. The researchers divided forty hospitalized patients who had just completed detox into two groups: one was assigned to stationary cycling at moderate intensity, the other, light intensity. The next day they switched the groups and found that intense exercise significantly reduced the urge for a drink. This is what happened with my patient Susan, from chapter 3, who used her jump rope to fend off the stress-induced urge to drink wine in the middle of the day.

The biology of stress ties in with addiction in that withdrawal puts the body in survival mode. If you suddenly quit drinking, for instance, you’re turning off the dopamine spigot and the hypothalamic-pituitary-adrenal axis gets thrown out of balance. The intense unpleasantness of withdrawal lasts for only a few days, but your system remains sensitive for much longer. If you’re in this delicate state and come under further stress, your brain interprets the situation as an emergency and sends you looking for more alcohol. That’s how a problem at work or a fight with a lover can cause a relapse. For someone who’s been dependant on drugs and has altered his dopamine system, the most effective solution to a stressful situation — and the only one he knows — is the drug. But exercise is another solution.

In smokers, just five minutes of intense exercise can be beneficial. Nicotine is an oddball among addictive substances as it works as a stimulant and a relaxant at the same time. Exercise fights the urge to smoke because in addition to smoothly increasing dopamine it also lowers anxiety, tension, and stress levels — the physical irritability that makes people so grouchy when they’re trying to quit. Exercise can fend off cravings for fifty minutes and double or triple the interval to the next cigarette. And the fact that exercise sharpens thinking comes into play here, because one of the withdrawal symptoms of nicotine is impaired focus. As evidence of this, one study found that there are more workplace accidents during the Great American Smokeout than on any other day of the year. Many of my ADHD patients use cigarettes to help them focus when they have to write or push through a challenging task, and without the nicotine they feel lost.

Some drugs, of course, dull the brain to begin with. A novel study from researchers in Iran recently examined how exercise affects rats on morphine. Their hypothesis was that since exercise influences dopamine and plasticity in the same brain areas involved with addiction and learning, maybe it would counteract the memory loss that goes along with being high. The scientists conditioned the rats by putting them in a dark box in which the floor shocked their feet, and then they did follow-up tests to measure how long it took the rats to move to another box that was harmless but well-lit (rodents prefer darkness).

The rats were divided into four groups: one group ran on a treadmill and received a shot of morphine before each trial; one ran and received a placebo injection of saline; another received morphine but didn’t exercise; and a control group received neither exercise nor an injection. Both groups that exercised remembered that the dark box was bad news: they hesitated the longest to enter it and were the quickest to leave when they were shocked. Amazingly, the exercise-and-morphine group performed better than the control group, indicating that exercise offsets the mind-dulling effects of the drug.

In the same study, the researchers found that exercise dramatically reduced withdrawal symptoms in the exercise-and-morphine group when they cut off the drugs — in rats, the signs of withdrawal are identified as “wet dog shakes,” writhing, and diarrhea. This fact alone should be enough to convince a recovering addict to lace up his sneakers, and it lends scientific credence to the treatment approach at Odyssey House.


Over the years, I’ve seen many people with reward-deficiency syndrome. The most dramatic example is a Dutch woman I’ll call Zoe, who suffers from severe ADHD and has a tumultuous history of depression, aggression, and a range of substance abuse. Most notably, she was a chronic marijuana smoker for twenty years who believed that self-medicating was the only way she could feel calm and focused.

In reality, she was trying to blot out the frustration and anger of her life. As a child, Zoe told me, she was combative and had severe learning problems. Now forty, she is still prone to tantrums and anxiety. On one occasion, when she was flying to Boston for a visit, she erupted in a panic attack and forced the plane to return to Amsterdam.

Zoe spent thirteen years getting through college, which is a long time even for her field of veterinary medicine, partly because she wasn’t diagnosed with ADHD until she was twenty-seven. She received a prescription for Ritalin but first had to go to a detox clinic to give up marijuana. “I was smoking ten or twenty joints a day,” she recalls. “When I was in there, I was like a wild animal in a cage.” She stopped smoking marijuana for about a year, but then she relapsed and soon fell back into her heavy habit of staying high throughout the day (while also taking the Ritalin and antidepressants).

Although she found a high-level job in her profession, Zoe stalled out in the decade after college and in many ways gave up on developing herself. Because she was always so driven to find an immediate reward, she didn’t set goals and strategies to move forward in life. Zoe often complained that she felt like life wasn’t worth it. Smoking marijuana, she says, kept her from dwelling on the fact that she was unhappy and discontent.

She had always exercised sporadically — cycling, sailing, and horseback riding — but I raised the subject of doing something on a regular basis. I appealed to her knowledge of medicine and explained how exercise could change her brain chemistry and rewire connections in the pathways controlling her mood, aggression, and attention as well as her addiction. After reading several of the studies I’ve included in this book, she committed to giving daily exercise a try, and she quit smoking marijuana again. “There was no alternative,” she says. “I had to do something.”

What she did was get an indoor bike trainer of the type used by serious cyclists to hone their balance and stamina — you pedal on free-spinning drums, acutely aware of the possibility that you could slip off and careen across the room. I’m not sure how Zoe settled on this extremely challenging form of exercise, but it has worked out tremendously well. The balance and precision required to ride on the rollers engages the entire attention system, from the motor centers of the cerebellum and basal ganglia to the reward center and prefrontal cortex. “At first I hated to do it because it doesn’t bring you anywhere,” she says. “Now I’m very handy on it, and it’s beneficial because it makes me concentrate as well as exercise. It’s exciting because you don’t want to fall down.”

As if kicking her habit wasn’t difficult enough, Zoe’s husband left her in the midst of her effort to stay sober, just before Christmas. I was worried, and so was she. “During the winter it gets cold and very dark in Holland,” she wrote in an e-mail. “I was so scared that I would get depressed again and go back on pot, but I haven’t. The change comes from the difference between feeling like a loser (smoking) and a winner (exercise).”

Zoe’s recovery is tenuous, as it is for any long-term drug user. But she’s certainly on the right track. She sends me regular updates about trying to break her record distance on the bike trainer, and she’s also taken up the jump rope. Here’s a snippet from one of her typically buoyant messages: “I just did 10 minutes of rope jumping, heart rate 140, exhausting but I had to do it. This is so GOOD, because in 10 minutes it feels like a half hour biking! Maybe I’ll continue this — it’s a FAST REWARD!!! It’s the exercise I’m craving nowadays.”


Some would debate whether Zoe was addicted to marijuana, but there’s no question she was dependent on it. She had all the signs of chemical dependency, including the physical and emotional irritability of withdrawal. Studies in rats show that if they get used to a chronic dose of tetrahydrocannabinol (THC) — the active compound in marijuana — and then are deprived of it, the brain floods the system with corticotropin-releasing factor, which activates the amygdala and thus the entire stress system. The rodents experience shaking, tremors, and twitchy movements that peak about forty-eight hours after the last dose. Indeed, Zoe felt like a rat in a cage when she went through detox: along with the physical symptoms, the shutdown of the dopamine system brought on intense feelings of depression and anxiety. The way exercise blunts the symptoms of withdrawal is by calming the amygdala and boosting dopamine.

Regardless of whether there is such a thing as marijuana addiction, studying THC’s effect on the brain has provided new clues about how exercise counteracts addiction of any stripe. To begin with, the feeling that often comes after exercise can serve as a harmless replacement for the drug high. In a recent study in the British Journal of Sports Medicine, researcher Arne Dietrich wrote that the way people describe runner’s high is “similar to the claims of distorted perception, atypical thought patterns, diminished awareness of one’s surroundings, and intensified introspective understanding of one’s sense of identity and emotional status made by people who describe drug or trance states.”

We’ve been on the case of the runner’s high for three decades, and in the last few years the focus has expanded beyond endorphins to include endocannabinoids, a class of neurotransmitters. Endocannabinoids are to THC as endorphins are to morphine — substances produced in the body that elicit the same effect as a drug. Likewise, they both dull pain.

Scientists discovered the endocannabinoids in the early 1990s after realizing that THC binds to specialized receptors in the brain. These receptors didn’t evolve for us to enjoy marijuana, obviously, so there had to be some natural substance the body produces for them. What they found were the neurotransmitters anandamide and 2-arachidonoylglycerol (2-AG). It turns out that marijuana, exercise, and chocolate all activate these same receptors in the brain.

Both of these endocannabinoids are produced in the body and the brain when we exercise. They travel through the bloodstream to activate receptors in the spinal cord, and this blocks pain signals from getting to the brain (not unlike morphine). They also move throughout the reward system and the prefrontal cortex, where they have a direct effect on dopamine. When the endocannabinoid receptors are strongly activated, they produce all the euphoric feelings of marijuana, and, along with endorphins, they act as the body’s extra-strength aspirin. Doctors are starting to use anandamide to treat pain syndromes such as chronic fatigue and fibromyalgia, and a number of studies have shown that gradually increasing exercise can relieve the pain and fatigue associated with these syndromes. The link between exercise and these natural pain killers makes perfect sense: they evolved to help us deal with the inevitable pain of straining muscles and joints during the hunt.

Unlike endorphins, endocannabinoids pass easily across the blood-brain barrier, which for some researchers, makes them a more plausible explanation for runner’s high. In 2003, a group led by psychologist Philip Sparling of Georgia Tech University showed for the first time that exercise activates the endocannabinoid system. Using fit, male college students either running on treadmills or cycling on stationary bikes for fifty minutes at 70 to 80 percent of their maximum heart rate, the researchers measured how the effort affected blood levels of anandamide. The result? Anandamide nearly doubled.

Runner’s high itself is difficult to study because it’s so unpredictable — even marathon runners don’t experience the feeling every time they train. And why isn’t there such a thing as swimmer’s high? One intriguing theory is based on the relatively new finding that there are endocannabinoid receptors in the skin that may be activated only by all the pounding and jostling of running. Regardless of whether the particular gauzy delirium of runner’s high kicks in, Sparling’s work clearly implies that the boost in anandamide is at least one reason we feel relaxed and satisfied after moderately intense exercise. Scientists still debate whether endorphins are involved, however, and it seems likely that the overall effect is some combination of these factors.


If exercise acts like certain drugs in the brain, then you might wonder whether it can also be addicting. I get this question all the time, and the short answer is yes, but don’t worry about it. Scientists have tested exercise addiction in rats and found that if they have unrestricted access to a running wheel and are given food only one hour a day, the rats will log about six miles a day and eventually run themselves to death. They don’t learn that they need to get all of their nutrition during their one-hour feeding. The more they run, the less they eat, and their calorie intake falls short of the output. They are addicted just as they would be to cocaine. Curiously, the experiment doesn’t work if a treadmill is substituted for the running wheel; perhaps there’s something about the infinite nature of chasing the next rung that keeps the rats hooked. Whatever the case, the running wheel is a perfect metaphor for addiction.

The danger of getting addicted to exercise applies to a very small segment of the population, most notably girls with anorexia or anyone with a body dysmorphic syndrome, a mental disorder defined by a preoccupation with a perceived deficit in appearance. They eat less and less, and when they exercise they become light-headed and exhilarated, the high only reinforcing the cycle. They feel great for a short while, and they think they are on their way to looking great. Sadly, their approach will never get them there. But for the vast majority of people, this trap is a remote danger. Even if exercise becomes a dependence — as it could for Zoe, for example — there’s little to worry about.

I can think of no better example of somebody with an exercise dependence than ultramarathoner Dean Karnazes, the forty-four-year-old Californian who has appeared on 60 Minutes, The Tonight Show, and countless magazine covers for his mind-bending feat of running fifty marathons in fifty days (in fifty different states). He also ran 350 miles without stopping. Only slightly less impressive to me is that over the past fifteen years, the longest period he has gone without exercising is three days. “I had the flu,” Karnazes recalls. “I was still sick, but I finally said, Screw it, I need to bust out a run.” For starters, his streak says something about the formidable strength of his immune system.

Karnazes was drunk at a bar on his thirtieth birthday when he decided to make a change in his life — at that very moment. He stumbled home, grabbed an old pair of sneakers, and ran thirty miles into the night. He was no alcoholic and has never been into drugs, but the question remains: does this guy have a problem? “Maybe 10 to 20 percent of the time I do think of running as an addiction,” he says. “What I really long for is the feeling of bliss or satiety that I get after exercise. It makes me feel complete. I’m most tuned into this when I can’t exercise. If I’m traveling or I’m in meetings all day, I can feel it pulling at me. I’ll think, Why am I ready to implode? I’m crawling out of my skin here! And then I realize my body needs to move. It’s almost a feeling of being trapped.”

There is no typical week for Karnazes, but he says he averages seventy to ninety miles — three to four hours on most days. In other words, he moves more in a day than most Americans do in a week. This frightens people. It would be easy to paint Karnazes as a freak of nature, and plenty of people have. When you talk to him, however, it seems that despite the huge time demand of training, he leads a balanced life. He held nine-to-five jobs at Fortune 500 companies for more than a decade, and then became president of a natural snack-food company, before recently transitioning into a professional athlete and author (his book, Ultramarathon Man, is a bestseller). He has two children, ages eleven and nine, whom he tucks in most every night and drives to and from school every day. He typically wakes up at around three a.m., after four or five hours of sleep, to get in his training before the kids need to go to school.

“I have built my lifestyle around running, so I can support this level of activity,” Karnazes says. “Perhaps it’s an addiction — I don’t know; I’ve never been through psychoanalysis. I’m just listening to my hardwiring. Luckily, I’m not shooting something in my veins or hopping down to the bar every night after work. Exercise is the ultimate drug, right? What drug always works and doesn’t have any unhealthy side effects?”


My patients, Rusty and Zoe are inspiring examples of people who have replaced addiction with exercise, instituting routines in their lives that serve as a healthy alternatives to the full-time pursuit of drugs. As I explained, the addict’s brain adapts at every level to focus attention and effort around getting the reward. The brain functions the same way whether the addiction is to alcohol, drugs, food, gambling, or any other addictive substance or behavior. As addiction progresses, there is less and less room for anything else in life.

When an addict quits, what’s left is emptiness. In this respect, dealing with addiction is similar to battling feelings of anxiety and depression: getting rid of the problem is only the first step. Once the addiction or the negative emotions are gone, the void needs to be filled with some positive behavior for the change to take root. There can hardly be a better option than physical exercise. After all, this is what we’re supposed to be doing — moving in the world.

The fact that exercise counteracts anxiety and depression directly can have a huge impact on any form of addiction, as both of these mood states undermine treatment. A recovering addict who is feeling anxious or hopeless is much more likely to slip in her determination and ability to quit. People are more impulsive when they feel lousy. Both strength training and aerobic exercise decrease symptoms of depression in recovering alcoholics and smokers who have quit. And as I pointed out in chapter 3, the more fit you are, the more resilient you are. If you are flexible in managing stress, you’re less likely to reach for that bottle of liquor or bag of chips or pack of cigarettes. Keeping the stress system under control is also important, practically speaking, for ameliorating the physical symptoms of withdrawal, to get through those nightmarish first few days.

Exercise also counteracts more direct toxic effects of addiction on the brain. Researchers looking at fetal alcohol syndrome, for instance, have shown that exposing unborn rats to high levels of alcohol dramatically reduces the birth of new brain cells in the hippocampus. It also disrupts long-term potentiation (LTP), the cellular mechanism of learning and memory. Studies of adult rats exposed to alcohol before birth suggest that they have difficulty learning.

The exciting news on this front is that both exercise and abstinence from alcohol not only stop the damage but also reverse it — increasing neurogenesis and thus regrowing the hippocampus of adult rats. The same holds true even for unborn rats if their mothers are taken off ethanol and allowed to run. In humans, researchers have recently shown that abstinence reverses some of the neuronal damage caused by prenatal exposure to alcohol, and we already know that exercise rebuilds the alcoholic brain by increasing neurogenesis.

One of the connections I see here is between learning and overall mental strength. If the brain is flexible, the mind is stronger, and this gets at a concept known as self-efficacy. It’s difficult to measure, but it relates to confidence in our ability to change ourselves. For most addicts, if they stop to consider how they may be destroying their lives, they suddenly feel like they can’t handle anything, let alone their self-control over their addiction. Exercise, though, can have a powerful impact on the way an addict feels about himself. If he’s engaged in a new pursuit such as exercise, which involves work and commitment, and he’s able to follow through and be persistent with it, that sense of self-control spreads to other areas of his life.

A group of Australian researchers recently put this idea to the test. Using twenty-four students as subjects, they measured the effect of a two-month exercise program on self-regulation, which is a slightly different characterization of self-efficacy. Every two weeks, the students were given two psychological tests, and they kept diaries of their daily habits. The results, published in 2006 in the British Journal of Health and Psychology, are profound. Aside from improving on the two tests, which measured intellectual inhibition (control), the participants reported that an entire range of behavior related to self-regulation took a turn for the better.

Not only did they steadily increase their visits to the gym, they reported that they smoked less, drank less caffeine and alcohol, ate more healthy food and less junk food, curbed impulse spending and overspending, and lost their tempers less often. They procrastinated less and kept more appointments. And, they didn’t leave the dishes in the sink — at least not as often.

The researchers characterized self-regulation as a resource that can be depleted but also recharged like a muscle. Essentially, the more you use this faculty, the stronger it gets. And exercise is by far the best form of self-regulation we have.


I wouldn’t suggest that you model your routine after that of Dean Karnazes, but if you have a tendency toward addictive behavior it’s vital to develop some sort of consistent exercise habit.

How much exercise you need depends, of course, on how severe the habit is. But I would say thirty minutes of vigorous aerobic exercise five days a week is the bare minimum if you want to root out an addiction. To begin, however, it’s best if you can do something every day, because the exercise will keep you occupied and focused on something positive. I have seen a lot of people who bury themselves in addiction when they lose their jobs, so if you are unemployed, having exercise in place is essential. And while I often suggest that people exercise in the morning, if your goal is to break a habit such as having a drink every night when you come home, exercising in the evening is probably a better strategy. You can use the aerobic shot for a different kind of buzz.

At the same time, you have to be careful not to overdo it and to find something you’ll be able to keep up over the long haul. The patients I’ve told you about all learned that aerobic exercise provides a strong reward, and they have been able to find that sense of satisfaction in a variety of activities. Rusty couldn’t do DDR all the time, so he got into soccer again and picked up rock climbing. Zoe started on the rollers, but as soon as spring hits she’s outside, riding her bike through the forest. The more options you have, the more likely you are to be able to continue exercising throughout your life.

If you haven’t been in the habit of exercising, it can be helpful to join a gym or hire a personal trainer, because spending the money is a strong motivator. If you have an addiction to food, try a quick walk around the block or a few minutes with a jump rope or even a set of thirty jumping jacks — anything to snap your mind out of the cycle of thinking about the reward.

It might sound painfully obvious to suggest exercise as a way of controlling your eating habits. After all, your weight is the sum of a simple formula — the number of calories you take in minus the number you burn. But it’s important to remember that exercise’s benefits go well beyond the physical aspect of burning calories. Dopamine produced during exercise will plug into receptors and thus blunt the craving, and over time the activity will produce more D2 receptors and restore balance in the reward system. For someone with a negative body image, shifting the focus from the body to the brain can provide a powerful new sense of motivation.

A lot of people assume that an addict’s real problem is just a lack of motivation. On one level, this is true, but what very few people recognize is that motivation is a function of brain signals, and that those signals depend on reliable messengers and intact nerve pathways. When we look at addiction as a neurological malfunction rather than as a moral failure, it suddenly takes on the form of something that can be fixed. It’s certainly not an easy task, but it’s a lot easier when we use exercise as a tool, one with great versatility. Exercise isn’t necessarily a cure, but it’s the only treatment I know of that works from the top down as well as from the bottom up, rewiring the brain to circumvent the addictive pattern and curbing the craving. Try it. Maybe you’ll get hooked.