Background This study examined the effect of a residential drug and alcohol therapeutic community program on criminal convictions among young people who had different trajectories of conviction prior to referral.

Method Data was derived from linked administrative records of all young people referred to a modified therapeutic community for serious alcohol and drug related difficulties located in New South Wales, Australia (n = 3059). Group-based trajectory modelling and propensity score matching estimated the potential treatment effect at age 17 on subsequent convictions up to 22 years of age, by three pre-referral trajectories of convictions from ages 10 to 16 years, designated “no or low convictions”, “moderate incline convictions”, and “high incline convictions”.

Results Treatment was associated with a significant decrease in convictions for only the high incline convictions trajectory after double adjustment of propensity scores and post-discharge incarceration. The reduction in the number of convictions for the high incline group was substantial (Cohen's d = 0.96), corresponding to 4.36 fewer convictions over five years post referral.

Conclusions Residential therapeutic communities may be an effective intervention to reduce future convictions among young people with drug and alcohol problems who have a high number of convictions prior to referral.