Cognitive Daily

ResearchBlogging.orgTeens who routinely exercise (especially in organized activities like team sports) are less likely to smoke or abuse drugs or alcohol. This fact alone might make it seem like a no-brainer to include physical activities in substance-abuse prevention and treatment programs, but in fact little research has been done to figure out whether exercising actually causes people to be less interested in drugs and alcohol. It’s also possible that potential substance-abusers are just uninterested in exercise, or that drug abuse causes a lack of interest in exercise. But because so little research has been done, it’s an open question: Should exercise be a part of drug abuse treatment programs?

One way to begin to address this question is in a controlled study with rats. Like humans, rats can become addicted to drugs, preferring them even to food and sex. When rats are trained to self-administer by pushing a lever, they’ll push it over and over again–even hundreds of times–to get a single dose of cocaine. So do rats who exercise use less drugs?

A team led by Mark Smith divided 17 female rats into two groups: Nine were placed in cages with exercise wheels, and 8 were in cages allowing only for sedentary activities (there’s no mention in the research report of whether they had sofas and TVs). A computer tracked the exercise levels of rats with exercise wheels: after few weeks, they averaged nearly 10,000 revolutions per day. Six weeks in, all the rats underwent surgery to implant a drug-injection catheter in their jugular veins. A week later, they were ready to start self-administering drugs.

To train a rat, the experimenter placed it in an operant conditioning chamber: a small plastic box with a lever at one end. A light lit above the lever indicating drugs were available to be administered. When the rat pressed the lever, it was injected with a dose of cocaine and the light shut off for 20 seconds. When the light reappeared, the rat could press the lever and get another dose. This was repeated daily until the rats could reliably self-administer 10 doses (for the rest of the day, all the rats were returned to their regular cages). Then the cycle was adjusted and rats were required to press the lever twice to get a single dose. Once they could do this, they were ready for testing.

During the testing phase, rats were placed in the chamber once a day, as before, but each time they received a dose, the number of lever-presses required to get the next dose increased rapidly: 1, then 3, then 6, 9, 12, 17, 24, 32, 42, 56, 73, 95, 124, 161, 208, 268, 346, 445, and 573. The key questions: how many times would a rat press the lever to get another dose, and was there any difference between the sedentary and exercising rats? Here are the results:


As you can see, sedentary rats gave themselves significantly more injections than the rats who were allowed to exercise. The researchers actually tested each rat with two different doses: 0.3 milligrams for every kilogram of weight (the rats averaged about 250 milligrams), and 1 mg per kg. Both groups were willing to work harder for larger doses, but in each case, the sedentary rats pressed the lever significantly more times. In the large-dose condition, sedentary rats pressed the lever an average total of 1,000 times per session, compared to just 270 for the exercising rats. They consumed fifty percent more cocaine than the active rats.

So does this mean that exercise can be an effective treatment for drug abuse? We can’t say for sure, but the connection is quite dramatic: Rats weren’t forced to exercise or to consume the drugs, but rats who were given the option of exercise chose to give themselves less cocaine. We know there are lots of other benefits of exercise in humans, from increasing in self-esteem and well-being to reduction in measures of depression. These would all seem to be important parts of a drug-treatment program, so it would certainly be worth it to try adding an exercise component to a drug-treatment program for humans to see if it helps.

Smith, M., Schmidt, K., Iordanou, J., & Mustroph, M. (2008). Aerobic exercise decreases the positive-reinforcing effects of cocaine Drug and Alcohol Dependence, 98 (1-2), 129-135 DOI: 10.1016/j.drugalcdep.2008.05.006


  1. #1 gs
    September 18, 2009

    “It’s also possible that potential substance-abusers are just uninterested in exercise, or that drug abuse causes a lack of interest in exercise.”

    The study does nothing to address this. It only confirms that rats who choose to be lazy also choose drugs — just like humans.

  2. #2 elliot
    September 18, 2009

    regarding the question of whether drug users are interested in exercise, i spend most of my 20′s running and smoking, as well as doing the occasional hallucinogen. It’s a great combination. But then I’m not a rat, so it isn’t clear to me that my experience would be relevant to the problem of drug use in rodents.

  3. #3 Roland
    September 18, 2009

    Many people “abuse drugs” as self-medication for emotional or other pain. Exercise releases endorphins. Exercise is known to reduce emotional depression. Side note: it seems particularly silly and evil to throw people in prison for self-medication for any type of pain. But that’s what this society does.

  4. #4 Nick
    September 20, 2009

    “The study does nothing to address this. It only confirms that rats who choose to be lazy also choose drugs — just like humans.”

    No.. In this study, the rats are randomly distributed to cages that have the exercise option and others that do not. Thus the setting determines whether the rat is sedentary or active, not the rat’s personal character.

  5. #5 Rebecca Jones
    September 21, 2009

    A better way would be to put the exercise wheels in all of the cages along with the option for cocaine. In my opinion the study shows correlation, but no causation. I think if a rat is in a cage hyped up on cocaine with nothing to do but pull a lever-then that is what he will do. If he is given a maze- he may try that too if he is high enough, what does that mean? That rats on cocaine are better problem solvers?

  6. #6 Fergus Ross Ferrier
    September 22, 2009

    Or perhaps the rats in the ‘sedentary’ cages were simply pressing the lever more as a substitute for exercise. Pushing the lever over a hundred times per hit [as would be happening once you get to the 12-hits level] must require some level of exertion, or the conclusions would have no force anyway.

  7. #7 Doug
    October 7, 2009

    Extending Fergus’s comment: perhaps the exercising rats were too tired to press the level as often as the sedentary rats.