The new study led by Mark A. Smith neuroscientist and Associate Professor from Davidson College has suggested that regular exercise can lower the tendency to become addicted to illegal drugs.

"We've known that individuals who engage in exercise have lower rates of substance abuse. But there were previously no data that showed a cause and effect relationship," said Smith

Over a two year period Smith and his three Davidson student research assistants- Karl Schmidt, Jordan Iordanou and Martina Mustroph 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 kilometres per day, while those without wheels got no exercise at all.

Later 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.

They 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.