The definition of success may vary from one rehab to another. So, it makes it difficult to measure the success rate of addiction rehab and treatment. Relapse is an incredibly common part of recovery, and it’s important to understand that returning to substance use does not mean treatment or recovery has failed. Effective treatment requires a multi-pronged approach that treats the person as a whole. Success also depends on the length of treatment; treatment of fewer than 90 days has limited effectiveness, while longer programming can have better long-term outcomes.