Drugs and alcohol cause fundamental changes in the way our brains work. When we use drugs and alcohol it affects the normal levels of dopamine and serotonin. Depending on the drug and depending on how long you have been using it, it could take anywhere from a couple of weeks to five or six months for the brain to repair. Some of the current research on marijuana is that recovery from heavy marijuana use, over any kind of extended period of time, can take as much as two years for all of your brain receptors to get back to the way that they are supposed to be. Cocaine and ecstasy can cause permanent brain damage.