PEARLS  323, August 2011, written by Brian R McAvoy 

Clinical question
How effective is motivational interviewing for reducing substance abuse? 

Bottom line
People who received motivational interviewing reduced their use of substances more than people who had not received any treat.ment. However, other active treatments, treatment as usual, and being assessed and receiving feedback were as effective as motivational interviewing. There was not enough data to form conclusions about the effects of motivational interviewing on re.tention in treatment, readiness to change, or repeat convictions. 

Caveat
The evidence was mostly of low quality. Motivational interviewing is a brief intervention. Given it involves only 1 to 4 sessions, one should not expect too much regarding changes in drug abuse outcomes. Motivational interviewing and other interventions share a number of non-specific therapeutic factors, such as attention and therapeutic alliance. These factors may have a much greater influence on outcome than the contribution made by approach-specific theory and technique. In an early review of empirical studies cited,common therapeutic factors accounted for 30% of the therapeutic effect, technique 15%, expectancy (placebo effect) 15%, and spontaneous remission 40%.1 

Context
There are 76.3 million people with alcohol use disorders world.wide and 15.3 million with drug use disorders. Motivational interviewing is a client-centred, semi-directive method for enhanc.ing intrinsic motivation to change by exploring and resolving ambivalence. The client and counsellor typically meet between 1 and 4 times for about 1 hour each time. The intervention is used widely, so, therefore, it is important to determine whether it helps, harms or is ineffective. 

Cochrane Systematic Review
Smedslund G, et al. Motivational interviewing for substance abuse. Cochrane Reviews, 2011, Issue 5. Article No. CD008063. DOI: 10.1002/14651858.CD008063.pub2. This review contains 59 studies involving 13,342 participants. 

Further references 1. Lambert, M. Handbook of Eclectic Psychotherapy. New York: Brunner Mazel; 1986:436Ð62.