What makes a faster-acting psychoactive drug produce more euphoria than a slower-acting one?
“The brain has many adaptive mechanisms, and if you disturb the brain slowly, it often can catch up or compensate,” explains Dr. George Uhl, who directs the Molecular Neurobiology Branch of NIDA’s Division of Intramural Research in Baltimore. “But, if you do things rapidly, often it can’t.” For example, going suddenly from a dark room into bright sunlight will result in a temporary loss of vision because the light sensitivity mechanisms of the eye and the brain cannot adapt that quickly, he says. But, if you proceed from dark to light slowly by stages, the mechanism works in a fairly automatic way, and you are able to see normally. “If a drug acts slowly, the brain is able to compensate for the changes that the drug produces,” says Dr. Uhl. However, when a drug’s onset of action is very rapid, it may be able to overwhelm the brain’s adaptive mechanisms, thus producing a bigger boost in its pleasure circuits, he says. Smoked and intravenous cocaine, for example, have fast rates of actio
