Summary of findings for the main comparison. Summary of findings ‐ 4 months or more of follow‐up.

Motivational interviewing versus no motivational interviewing (assessment only or alternative intervention) for prevention of alcohol misuse
Patient or population:young adults aged up to 25 years Settings: education, health, criminal justice or community settings Intervention: motivational interviewing Comparison: no intervention/placebo/treatment as usual Follow‐up: ≥ 4 months Measurement: self reported alcohol consumption (questionnaire scale)
Outcomes	Illustrative comparative risks* (95% CI)		Relative effect (95% CI)	No of participants (studies)	Quality of the evidence (GRADE)	Comments
	Assumed risk	Corresponding risk
Quantity of alcohol consumed	The mean number of drinks per week was 13.74 in the control group, with a standard deviation of 10.77, from the DDQ measure in Martens 2013	The SMD from the meta‐analysis (−0.11) corresponds to a decrease of 1.2 drinks consumed each week (95% CI 0.7 to 1.6), from an average of 13.7 drinks per week to 12.5 drinks per week, based on Martens 2013	SMD −0.11 (−0.15 to −0.06)	7971 (33)	⊕⊕⊕⊝ Moderate	Downgraded 1 level due to risk of bias
Frequency of alcohol consumption	The mean drinking days per week was 2.74 in the control group, with a standard deviation of 1.54, from the DDQ measure in Martens 2013	The SMD from the meta‐analysis (−0.14) corresponds to a decrease of 0.22 drinking days per week (95% CI 0.11 to 0.32), from an average of 2.74 drinking days per week to 2.52 drinking days per week, based on Martens 2013	SMD −0.14 (−0.21 to −0.07)	4377 (17)	⊕⊕⊕⊝ Moderate	Downgraded 1 level due to risk of bias
Binge drinking	Binge drinking frequency in the previous month was 5.05 at baseline for the whole sample, with a standard deviation of 4.53, in the study by Carey 2011	The SMD from the meta‐analysis (−0.04) corresponds to a decrease in binge drinking frequency in the previous month of −0.2 binge drinking occasions (95% CI −0.4 to 0.1), from an average of 5.1 occasions to 4.9 occasions per week, based on Carey 2011.	SMD −0.04 (−0.09 to 0.02)	5479 (21)	⊕⊕⊕⊝ Moderate	Downgraded 1 level due to risk of bias
Alcohol problems	The mean alcohol problems scale score was 8.91 in the control group, with a standard deviation of 9.17 (the 69‐point RAPI scale used by Martens 2013)	The SMD from the meta‐analysis (−0.08) corresponds to a decrease of 0.73 on the alcohol problems scale score (95% CI 0.00 to 1.56), from an average of 8.91 to 8.18, based on Martens 2013	SMD −0.08 (−0.17 to 0.00)	6868 (25)	⊕⊕⊝⊝ Low	Downgraded 2 levels due to high heterogeneity (I2 = 58%) and risk of bias
Average BAC	The average BAC was 0.082% at baseline for the whole sample, with a standard deviation of 0.057, in the study by Carey 2011	The SMD from the meta‐analysis (−0.05) corresponds to a decrease of −0.003 for average BAC (95% CI −0.010 to 0.005), from an average of 0.082% to 0.079%, based on Carey 2011	SMD −0.05 (−0.18 to 0.08)	901 (5)	⊕⊕⊕⊝ Moderate	Downgraded 1 level due to risk of bias
Peak BAC	The mean peak BAC was 0.144% in the control group, with a standard deviation of 0.111, from the DDQ measure in Martens 2013	The SMD from the meta‐analysis (−0.12) corresponds to a decrease of 0.013 for peak BAC (95% CI 0.006 to 0.025), from an average of 0.144% to 0.131%, based on Martens 2013	SMD −0.12 (−0.20 to −0.05)	2790 (13)	⊕⊕⊕⊝ Moderate	Downgraded 1 level due to risk of bias
Drink‐driving	The number of drink‐driving occasions in the previous 12 months was 7.8 at baseline in the control group, with a standard deviation of 16.9, from the DrInC‐2L measure, in Schaus 2009	The SMD from the meta‐analysis (−0.13) corresponds to a decrease of −2.2 drink‐driving occasions (95% CI −6.1 to 1.7), from an average of 7.8 to 5.6, based on Schaus 2009	SMD −0.13 (−0.36 to 0.10)	1205 (4)	⊕⊕⊕⊝ Moderate	Downgraded 1 level due to high heterogeneity (I2 = 61%)
Risky behaviour	The number of times foolish risks were taken in the previous 12 months was 6.6 at baseline in the control group, with a standard deviation of 11.9, from the DrInC‐2L measure, in Schaus 2009	The SMD from the meta‐analysis (−0.15) corresponds to a decrease of −1.8 risk taking occasions (95% CI −3.7 to 0.1), from an average of 6.6 to 4.8, based on Schaus 2009	SMD −0.15 (−0.31 to 0.01)	1579 (7)	⊕⊕⊕⊝ Moderate	Downgraded 1 level due to risk of bias
*The basis for the assumed risk is provided in footnotes. The corresponding risk (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). BAC: blood alcohol concentration; CI: confidence interval; SMD: standardised mean difference; DDQ: Daily Drinking Questionnaire; RAPI: Rutgers Alcohol Problems Index.
GRADE Working Group grades of evidence High quality: Further research is very unlikely to change our confidence in the estimate of effect. Moderate quality: Further research is likely to have an important impact on our confidence in the estimate of effect and may change the estimate. Low quality: Further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate. Very low quality: We are very uncertain about the estimate.

In the columns illustrating comparative risks: for outcomes where the pooled analysis point estimate and confidence interval showed some effect, we have used results (mean scores and standard deviations) from Martens 2013 to illustrate the effect sizes in terms of the measures used in that study. We chose Martens 2013 because the outcome measures they use are well known, generally well regarded, and are typical of the measures used in this field of research: they used the Daily Drinking Questionnaire (DDQ) and the Rutgers Alcohol Problems Index (RAPI). For similar reasons, we used Carey 2011 as a basis for illustrating effect sizes for binge drinking, as they also based their measures on the DDQ, and Schaus 2009 as they used the Drinker Inventory of Consequences (DrInC‐2L; Miller 1995b). Furthermore, the sample sizes were typically larger than similar studies with potentially more reliable indication of variance (SD) for relevant outcomes.