We aimed to assess the effectiveness of drug tests for treatment retention in outpatients starting opioid substitution therapy. A retrospective cohort was created from the data of the French health insurance system database for the Midi-Pyrenees region. Patients starting opioid substitution treatment (OST) were included and followed for 18 to 30 months. Two groups of patients were defined: the drug test group (at least one drug test reimbursement) and a control group (no drug test reimbursement). The cohort included 1507 patients. During follow-up, 39 subjects (2.6%) had at least one drug test reimbursement. Mean treatment retention was 207 days in the control group and 411 days in the drug test group (p < 0.001). With a multivariate Cox model, drug tests were associated with treatment retention: hazard ratio 0.55 (95% CI: 0.38-0.80). Use of a drug test in follow-up of opioid substitution treatment, although rarely prescribed, significantly improved treatment retention.
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