“…Findings, drug use. Thirty-four studies (47.2%) [39, 42, 46, 49, 53, 58, 63, 64, 68, 71, 72, 75, 77, 79-82, 84, 85, 87-89, 91-95, 97-99, 101, 104, 108, 109] assessed the use of illicit drugs (as described by the study authors) either through urinalysis (n = 18/34, 52.9%) [53, 58, 63, 71, 72, 79, 80, 85, 87, 89, 93-95, 97, 98, 101, 104, 109] or through self-report measures (n = 16/34, 47.0%) [39,42,46,49,64,68,75,77,81,82,84,88,91,92,99,108]. Most studies (n = 21/34, 61.8%) [42, 46, 49, 53, 58, 63, 64, 72, 75, 80, 81, 84, 85, 87-89, 91-95, 97, 98, 101, 104, 109] were designed with a counselling [53, 63, 72, 80, 85, 87, 89, 93-95, 97, 98, 101, 104] or OAT-only [58,94,109] control group.…”