Research by a Davidson College neuroscientist and students demonstrates that the benefits of regular exercise include a lowered tendency to become addicted to illegal drugs, and they suspect the exercise benefit may be from increasing release of dopamine in the brain.

The online version of the journal Drug and Alcohol Dependence published this week the results of the study by Associate Professor Mark A. Smith that shows that exercise can help prevent drug addiction.

Smith said his research provides scientific validity for a long-standing suspicion among drug abuse researchers that exercise plays a role in helping people avoid and overcome drug addiction. “We’ve known that individuals who engage in exercise have lower rates of substance abuse,” said Smith. “But there were previously no data that showed a cause and effect relationship.”

Smith’s findings take on added importance in light of a newly announced initiative by the National Institute of Drug Abuse (NIDA) to support research on exercise and drug abuse. Recent studies show that about 20 million Americans age 12 and older (about 8.3% of the population) have used an illicit drug in the past month. Speaking at a NIDA conference June 4-5, 2008, director Dr. Nora Volkow committed $4 million for studies about the effect of exercise on drug use. Smith’s Davidson research was not published until after the NIDA conference.

Smith and his students compared the tendency to self-administer cocaine between two groups of rats. One group of rats lived in laboratory cages equipped with a running wheel, and the other group lived in a standard cage with no wheel. During six weeks, the rats in the wheel cages increased their running to about 10 kilometers per day, while those without wheels got no exercise at all.

At the end of six weeks, all the rats were connected to an infusion pump that would provide a dose of cocaine if they pushed a lever in their cage. However, the number of pushes necessary to deliver a dose increased geometrically for each subsequent dose.

The researchers found that the fit rats abandoned the task when 70 lever presses were required for a cocaine infusion. However, sedentary rats kept pushing the lever even when 250 lever presses were required for an infusion. In addition, the rats that ran the most on the wheel abandoned the task at a lower number of pushes than their fellow exercising rats.

“We concluded that aerobic exercise reduces the rewarding effects of cocaine, and probably also has protective effects against cocaine abuse.” Smith said. “That shows me that in the real world, exercise can be an effective intervention in drug abuse prevention and treatment programs. As a treatment, it’s widely available, easy to execute, inexpensive, and feasible for use in diverse patient populations. In addition, its principle side effects are all positive - weight loss, lower blood pressure, and increased confidence and self-esteem.”

Smith said exercise works because both exercise and illicit drugs prompt the same release in the brain of the euphoria-inducing protein, dopamine. Long-term exercise alters the number of dopamine receptors in the brain, meaning that drugs then have less of a euphoric effect.

Smith said he expects other researchers to begin working on exercise studies with human patients. His subsequent project at Davidson, however, will determine whether exercise can help mitigate the effects of relapse to drug use among rats.

Smith believes exercise can prevent not only addiction to cocaine, but other drugs as well since they all affect dopamine levels. In the future, he plans to conduct a similar study at Davidson with heroin.

Smith is enthusiastic about the contribution of his study. He said, “Exercise has long been known to produce positive cardiovascular effects. We’re now also finding that it has positive psychological effects as well, in the treatment and prevention of drug abuse, depression, and anxiety disorders. I think there’s even more and we’re just beginning to scratch the surface” (Newswise).