UCLA

Stimulant use rates are higher among men who have sex with men (MSM) than the general population. Contingency management (CM) may be an effective intervention for reducing stimulant use in this population. To specify both the mechanism and temporal effects of contingent reward on behavior change, logistic growth trajectory modeling (LGTM) was used to contrast a non-contingent matched rewards condition (i.e., non-contingent yoked controls; NCYC) to a voucher-based CM intervention (maximum=$430) to reduce stimulant use among MSM. Stimulant-using MSM were randomized to either a CM intervention (n=70) or a NCYC condition (n=70). Results from a LGTM (analytical sample n=119; n_CM=61; n_NCYC=58) indicated four distinct intervention response patterns: responders (i.e., predicted >90% stimulant metabolite-free urinalyses; 64.7% of sample); worsening intervention response (14.3%); non-responders (12.6%); and, single-positive (8.4%); all estimated trajectory coefficients were significant at p<0.03 (2-tailed). Participants receiving CM were significantly overrepresented in the responder (64%) and single-positive (80%) categories (χ²₍₃₎=29.04; p<0.001); all non-responders and 76.5% of the worsening intervention response category were in the NCYC condition. Results demonstrate the utility of trajectory modeling and further support the contingent application of reward as the operative mechanism associated with patterns of stimulant abstinence with CM applied to a sample of stimulant-using MSM outside the context of formal drug treatment.