Experimental Groups All participants were invited to attend the therapeutic workplace for 26 weeks. Prescription group participants were provided a take-home supply of oral naltrexone every 30 days and were allowed to access the workplace independent of naltrexone ingestion. Contingency participants were required to ingest oral naltrexone under staff observation every Monday, Wednesday, and Friday to gain access to the workplace. Contingency participants who missed a naltrexone dose were not permitted to access the workplace until they were able to resume naltrexone. Additionally, missing a scheduled dose resulted in a base pay reset from $8 per hour to $1 per hour. After a reset a participant's base pay increased by $1 per hour to a maximum of $8 per hour for every day that a participant attended the workplace for at least 5 minutes.