Mandatory Rehab is effective by helping drug addicts reduce their criminal activities and improve their socializing skills. Another article shows that rehab is 45% more effective than other therapy methods. 

Rehab can help drug users by informing them what drugs can do to a person and their family. Rehab can also help rebuild relationships from before and after they started using drugs. Since some people start using drugs because of depression or family problems, rehab has emotional support to help them talk about their problems and help them not use drugs anymore.