Rosemarie Schwenker and colleagues recently published their review titled " Motivational interviewing for substance use reduction". You can read the Plain Language Summary below or access the full review on the Cochrane Library.

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.