Simpson, D. D., Joe, G. W., & Broome, K. M. (2002).  A national 5-year follow-up of treatment outcomes for cocaine dependence.  Archives of General Psychiatry, 59, 538-544.

Abstract:  Background: Long-term (5-year) outcomes of community treatment for cocaine dependence were examined in relation to problem severity at treatment entry and treatment exposure throughout the follow-up period.  Methods: Interviews were conducted at 1 and 5 years after treatment for 708 subjects (from 45 programs in 8 cities) who met DSM-III-R criteria for cocaine dependence when admitted to treatment in 1991-1993.  Primary outcome measures included cocaine use and arrests.  Self-reported cocaine use showed high overall agreement with urine (79% agreement) and hair (80% agreement) toxicology analyses.  Results: Weekly cocaine use was reported by 25% of the sample at 5 years, slightly higher than the 21% at 1 year.  Similarly, 26% had cocaine detected in urine specimens at follow-up and 18% reported having been arrested.  Poorer long-term outcomes were related to higher problem severity at treatment admission and low treatment exposure.  Conclusions: The large decreases in cocaine use 1 year after treatment discharge were sustained during the 5-year follow-up.  Severity of drug and psychosocial problems at intake was predictive of long-term outcomes and outcomes improved in direct relation to level of treatment exposure.