Summary of main results
Extent of substance abuse
The main finding of this review is that compared to a no treatment
control MI has shown a significant effect on extent of
substance abuse. The effect was strongest at post-intervention
SMD 0.79 (95%CI 0.48 to 1.09) and weaker at short follow-up
SMD0.17 (95%CI 0.09 to 0.26]), and medium follow-up SMD
0.15 (95%CI 0.04 to 0.25]). For long follow-up, the effect was
not significant SMD 0.06 (95%CI -0.16 to 0.28).
MI did better than assessment and feedback for medium followup
regarding extent of substance abuse SMD 0.38 (95%CI0.10,
0.66]). For short follow-up, there was no significant effect of MI
SMD 0.12 (95% CI -0.01 to 0.24]). We found no data on the
effect of MI vs assessment and feedback for post-treatment or for
follow-up times longer than 12 months.
There was no significant difference between MI and other active
intervention at any follow-up time on extent of substance abuse.
Neither was there a difference betweenMI and treatment as usual.
Type of substance and level of substance use
We were interested in studying whether MI is more effective in
treating abuse of one type of substance (e. g. alcohol) versus other
types of substances (e.g. cocaine), but there were not enough studies
to perform such comparisons. We also wanted to summarize
possibly different effects of MI on severe abuse versus less severe
abuse, but we were not able to assess severity across studies from
the available information reported in the included articles.
Secondary outcomes
Therewere not enough data to conclude about the effects ofMI on
retention in treatment, readiness to change, or repeat convictions.