THE EFFECTS OF A MONETARY ALTERNATIVE ON MARIJUANA SELF-ADMINISTRATION

The availability of alternative reinforcers can reduce drug self-admin istration. This 21-day residential study investigated the effect of mo netary alternatives on marijuana self-administration. Three female and four male participants performed computer tasks (baseline) in the mor ning before smoking a sample marijuana cigarette (0.0, 1.8, or 3.9% De lta(9)-tetrahydrocannabinol (THC)) and receiving the sample alternativ e ($5.00 voucher). In the afternoon, participants had five opportuniti es to choose either the marijuana cigarette sampled earlier or a vouch er for $5.00. Participants were required to meet a criterion level of task performance to obtain each choice. The monetary performance crite rion varied from day to day (80, 100, or 120% of baseline); the mariju ana performance criterion remained constant at 100% of baseline. Choic es were delivered in the evening, after task completion. Marijuana cho ice varied as a function of THC concentration and criterion to earn mo ney. Active marijuana was always chosen more often than placebo, and a ctive and placebo marijuana mere chosen over money when the criterion to earn money was high. Task performance improved when criteria were i mposed, even after participants had smoked the sample marijuana cigare tte. Subjective ratings of drug effects increased with increasing THC concentration, but did not predict choice. The availability of a monet ary alternative was effective in shifting choice to self-administer ma rijuana, and marijuana choice was sensitive to contingency manipulatio ns. The results further indicate that contingency manipulations may ov erride the performance-impairing effects of marijuana observed in othe r studies.