Exercise may make it more difficult to break an addiction in some cases, a study of cocaine-addicted mice suggests.
The study included male mice, some of whom had running wheels in their cages. After 30 days, the mice were placed in small chambers, and given liquid cocaine.
All of the mice showed a preference for the place within their chamber where they received cocaine, The New York Times reports. Some of the animals that had not previously had running wheels were given them, while the ones who already had the wheels were allowed to continue using them.
The researchers stopped giving the mice cocaine, and watched how long it took them to stop returning to the spot where they had received the cocaine, a sign thought to indicate that an animal has overcome its addiction.
The mice that had started the study as non-exercisers, and only started running after they became addicted, stopped going to their preferred spot quickly and easily. The mice that had been running since the beginning of the study took a longer time to stop returning to that spot, and many did not stop at all.
Researcher Justin S. Rhodes of the University of Illinois said the study should not discourage people from exercising if they are combating addiction. He pointed out there are a number of other studies that have shown exercise appears to stimulate reward centers in the brain that might substitute for drug cravings.
The study appears in The European Journal of Neuroscience.