The more reinforcing a stimulus is the more a person is willing to sacrifice to re-experience it. Cocaine and amphetamine are the most reinforcing stimuli known. It generally takes 2 to 4 years between the initial exposure to the stimulant and the development of addiction. 1 Repeated drug exposure has long term consequences for the nervous system. Drug tolerance one example of a neuroadaptation in which a progressively greater dose of the drug is required to achieve the same effect.
Tolerance is generally reversible with extended abstinence.
More sinister is sensitization, which refers to increasing sensitivity to certain drug effects with repeated doses, and may be partially irreversible. Sensitization is thought to be responsible for the development of the compulsive aspect stimulant addiction, and so is responsible for sham reward . Sensitization is more likely to occur with intermittent dosing, while tolerance is more likely to occur with steady dosing. In contrast to the steady pattern of consumption that characterize alcohol and opiate use, an intermittent pattern of consumption is more typical among stimulant abusers. The absence of daily use does not indicate decreased compulsion .