OMT patients from 7 clinics who were using cocaine , benzodiazepines , heroin or amphetamines were randomly allocated to either treatment as usual ( n = 64 ) or treatment with an additional escalating reinforcement scheme ( n = 72 ) in which a patient 's number of weekly take-home dosages was increased after 1 , 4 , 8 and 12 consecutive weeks with drug-free urine specimens .