Cardiovascular and subjective effects of repeated smoked cocaine administration in experienced cocaine users.

Studies using rodents have shown that behavioral responses to a stimulant are enhanced when the stimulant is given within the same context as previous stimulant administrations; this increase in effect related to context is often referred to as sensitization. We examined the role of environmental stimuli in modulating the subjective and cardiovascular effects of cocaine in humans (1) within a daily "binge" and (2) after cocaine abstinence. Ten non-treatment seeking users of smoked cocaine were admitted to the hospital for 17 consecutive days. Participants smoked cocaine (25mg/dose) under two counterbalanced conditions: paired stimuli (same stimuli presented each session) and unpaired stimuli (varied stimuli presented each session). Under each stimulus condition, participants had cocaine test sessions for three consecutive days, no sessions for the next 3 days, then another cocaine test session on the following day, for a total of eight test days. Stimulus condition had no effect on cardiovascular or subjective effects so data were analyzed as a function of repeated cocaine administration over 2 weeks. Maximal ratings on "good drug" and "drug rating" subjective effects clusters decreased over days of repeated cocaine exposure. In contrast, baseline and peak heart rate and systolic pressure increased over days of repeated cocaine administration. Thus, repeated administration of smoked cocaine to experienced cocaine users resulted in increases in baseline blood pressure and heart rate and modest decreases in positive subjective effects. These data indicate modest tolerance rather than sensitization to the positive subjective effects of cocaine with repeated exposure.