• Contingency management;
  • difference-in-differences;
  • health services utilization


Aim  To determine the impact of standard care and contingency management treatments on the utilization of general health-care services by substance abusers.

Participants, design and measurements  This secondary analysis pooled 1028 treatment-seeking substance abusers from five randomized clinical trials that compared the effects of standard care (SC, n = 362) to standard care plus contingency management (CM, n = 666). In each trial, subjects in the CM condition showed significantly greater reductions in substance use than their SC counterparts. For each subject, utilization of 15 general health-care services was measured 1 year prior to treatment intake and up to 9 months following treatment intake. Post-intake utilization data were prorated to be comparable to the 1-year pre-intake data. Paired t-tests evaluated changes in service utilization pre- and post-intake, and difference-in-differences regression models were used to estimate the impact of CM, compared to SC, on changes in the utilization of each of the 15 health services.

Setting  Out-patient community substance abuse clinics in Connecticut and Massachusetts, USA.

Findings  Utilization of several types of out-patient services increased significantly between the pre- and post-intake periods [e.g. dental visits (0.47, P < 0.001), community health center visits (0.50, P < 0.001), visits to a mental health professional office (1.03, P = 0.001)], while in-patient hospital care for mental health problems decreased significantly (−3.50 nights, P < 0.001). A substantial portion of these changes occurred during the treatment period. No significant differences were found between the two treatment conditions.

Conclusions  Initiating out-patient substance abuse treatment is associated with changes in general health-care service utilization, independent of the type of treatment offered.