Key messages
• Motivational interviewing may reduce substance use compared with no intervention for a short time.
• We have moderate to no confidence in the evidence, which forces us to be careful about our conclusions. New research may change our conclusions.
• Future studies comparing motivational interviewing to other treatments should be larger, better designed, and better reported.
What is substance use?
'Substance use' refers to the consumption of drugs or alcohol, which can have various effects on the mind and body. Substance use can have a number of consequences, including addiction, physical and mental health problems, and social and legal issues. Alcohol and drugs are therefore potentially harmful substances. People who use substances can damage their health and become ill as a result. About 30 to 35 million people are ill because they use substances. Substance-use disorders are now recognised as complex conditions related to psychosocial, environmental, and biological factors.
How is substance use (or substance-use disorder) treated?
There are a variety of treatments. Our review focused on motivational interviewing, which is a type of counselling aimed at helping people find the motivation to reduce or stop their substance use. Motivational interviewing involves a conversation between a trained counsellor and a client. The two usually meet 1 to 4 times for about an hour each. In the sessions, the counsellor helps the person explore the reasons that prevent them from giving up substance use. The counsellor helps them find ways to feel more willing, able, and confident to reduce or stop using substances, instead of telling the person why and how to change their behaviour.
What did we want to find out?
We wanted to find out whether motivational interviewing is better than no treatment or other forms of treatment at helping people to reduce or stop substance use. We also wanted to find out if motivational interviewing affects people's willingness to change and whether they stay in treatment.
What did we do?
We looked for studies involving people who used substances such as alcohol or drugs. In the studies, people were divided by chance into a motivational interviewing group and a 'control' group that received either no treatment, regular treatment, assessment and feedback, or another active treatment.
Regular treatment involved sharing screening results, advising people to stop using alcohol/drugs, and providing educational materials. Assessment and feedback involved giving people relevant reading material and the chance to ask questions, but no counselling. Other active treatments varied; providing an educational programme about drugs and alcohol is a typical example.
We compared and summarised the results of the studies, and rated our confidence in the evidence, based on factors such as study methods and sizes.
What did we find?
We found 93 studies that involved 22,776 people with substance use. The largest study involved 1726 people and the smallest involved 25 people. The studies were conducted in countries around the world; most were in the USA (72). In most studies (30), one motivational interviewing session was conducted. There were also studies in which more sessions were conducted, up to 9 sessions. Session durations varied, from as little as 10 minutes to as long as 148 minutes per session.
The results show that motivational interviewing may make little to no difference to substance use compared with regular treatment or another active intervention. However, in the short term, motivational interviewing may reduce substance use compared with no treatment. At medium- and long-term follow-up, motivational interviewing probably reduces substance use slightly compared with assessment and feedback. It is unclear whether motivational interviewing has an effect on willingness to change and staying in treatment.
What are the limitations of the evidence?
We have moderate to no confidence in the evidence because of concerns about how some of the studies were conducted. The results were very inconsistent across the different studies, and 18 of the studies involved fewer than 100 people. The certainty of the research forces us to be careful about our conclusions; new research may change them.
How up to date is this evidence?
The evidence is current to November 2022.
Motivational interviewing may reduce substance use compared with no intervention up to a short follow-up period. MI probably reduces substance use slightly compared with assessment and feedback over medium- and long-term periods. MI may make little to no difference to substance use compared to treatment as usual and another active intervention. It is unclear if MI has an effect on readiness to change and retention in treatment. The studies included in this review were heterogeneous in many respects, including the characteristics of participants, substance(s) used, and interventions. Given the widespread use of MI and the many studies examining MI, it is very important that counsellors adhere to and report quality conditions so that only studies in which the intervention implemented was actually MI are included in evidence syntheses and systematic reviews. Overall, we have moderate to no confidence in the evidence, which forces us to be careful about our conclusions. Consequently, future studies are likely to change the findings and conclusions of this review.
Substance use is a global issue, with around 30 to 35 million individuals estimated to have a substance-use disorder. Motivational interviewing (MI) is a client-centred method that aims to strengthen a person's motivation and commitment to a specific goal by exploring their reasons for change and resolving ambivalence, in an atmosphere of acceptance and compassion. This review updates the 2011 version by Smedslund and colleagues.
To assess the effectiveness of motivational interviewing for substance use on the extent of substance use, readiness to change, and retention in treatment.
We searched 18 electronic databases, six websites, four mailing lists, and the reference lists of included studies and reviews. The last search dates were in February 2021 and November 2022.
We included randomised controlled trials with individuals using drugs, alcohol, or both. Interventions were MI or motivational enhancement therapy (MET), delivered individually and face to face. Eligible control interventions were no intervention, treatment as usual, assessment and feedback, or other active intervention.
We used standard methodological procedures expected by Cochrane, and assessed the certainty of evidence with GRADE. We conducted meta-analyses for the three outcomes (extent of substance use, readiness to change, retention in treatment) at four time points (post-intervention, short-, medium-, and long-term follow-up).
We included 93 studies with 22,776 participants. MI was delivered in one to nine sessions. Session durations varied, from as little as 10 minutes to as long as 148 minutes per session, across included studies. Study settings included inpatient and outpatient clinics, universities, army recruitment centres, veterans' health centres, and prisons.
We judged 69 studies to be at high risk of bias in at least one domain and 24 studies to be at low or unclear risk.
Comparing MI to no intervention revealed a small to moderate effect of MI in substance use post-intervention (standardised mean difference (SMD) 0.48, 95% confidence interval (CI) 0.07 to 0.89; I2 = 75%; 6 studies, 471 participants; low-certainty evidence). The effect was weaker at short-term follow-up (SMD 0.20, 95% CI 0.12 to 0.28; 19 studies, 3351 participants; very low-certainty evidence). This comparison revealed a difference in favour of MI at medium-term follow-up (SMD 0.12, 95% CI 0.05 to 0.20; 16 studies, 3137 participants; low-certainty evidence) and no difference at long-term follow-up (SMD 0.12, 95% CI -0.00 to 0.25; 9 studies, 1525 participants; very low-certainty evidence). There was no difference in readiness to change (SMD 0.05, 95% CI -0.11 to 0.22; 5 studies, 1495 participants; very low-certainty evidence). Retention in treatment was slightly higher with MI (SMD 0.26, 95% CI -0.00 to 0.52; 2 studies, 427 participants; very low-certainty evidence).
Comparing MI to treatment as usual revealed a very small negative effect in substance use post-intervention (SMD -0.14, 95% CI -0.27 to -0.02; 5 studies, 976 participants; very low-certainty evidence). There was no difference at short-term follow-up (SMD 0.07, 95% CI -0.03 to 0.17; 14 studies, 3066 participants), a very small benefit of MI at medium-term follow-up (SMD 0.12, 95% CI 0.02 to 0.22; 9 studies, 1624 participants), and no difference at long-term follow-up (SMD 0.06, 95% CI -0.05 to 0.17; 8 studies, 1449 participants), all with low-certainty evidence. There was no difference in readiness to change (SMD 0.06, 95% CI -0.27 to 0.39; 2 studies, 150 participants) and retention in treatment (SMD -0.09, 95% CI -0.34 to 0.16; 5 studies, 1295 participants), both with very low-certainty evidence.
Comparing MI to assessment and feedback revealed no difference in substance use at short-term follow-up (SMD 0.09, 95% CI -0.05 to 0.23; 7 studies, 854 participants; low-certainty evidence). A small benefit for MI was shown at medium-term (SMD 0.24, 95% CI 0.08 to 0.40; 6 studies, 688 participants) and long-term follow-up (SMD 0.24, 95% CI 0.07 to 0.41; 3 studies, 448 participants), both with moderate-certainty evidence. None of the studies in this comparison measured substance use at the post-intervention time point, readiness to change, and retention in treatment.
Comparing MI to another active intervention revealed no difference in substance use at any follow-up time point, all with low-certainty evidence: post-intervention (SMD 0.07, 95% CI -0.15 to 0.29; 3 studies, 338 participants); short-term (SMD 0.05, 95% CI -0.03 to 0.13; 18 studies, 2795 participants); medium-term (SMD 0.08, 95% CI -0.01 to 0.17; 15 studies, 2352 participants); and long-term follow-up (SMD 0.03, 95% CI -0.07 to 0.13; 10 studies, 1908 participants). There was no difference in readiness to change (SMD 0.15, 95% CI -0.00 to 0.30; 5 studies, 988 participants; low-certainty evidence) and retention in treatment (SMD -0.04, 95% CI -0.23 to 0.14; 12 studies, 1945 participants; moderate-certainty evidence).
We downgraded the certainty of evidence due to inconsistency, study limitations, publication bias, and imprecision.