Exploring the performance of during-treatment substance use outcome measures in predicting longer-term psychosocial functioning and post-treatment abstinence

•Duration of abstinence during treatment predicts longer-term functioning improvement.•Effects are consistent across different primary substance groups.•Effect of end-of-treatment abstinence on post-treatment outcomes is stable over time.•This endpoint may be a particularly reliable indicator of treatment success.•Complete abstinence during treatment was not consistently associated with functioning.