Key messages

• Liraglutide compared with placebo (a sham medication) likely increases the number of people who lose at least 5% of their body weight, but its impact on unwanted effects, quality of life, and major cardiovascular events appears small or uncertain over both the medium term (6 to 24 months) and long term (more than 24 months).

• Our confidence in the evidence is limited due to how the studies were done and missing information. The manufacturers of liraglutide were involved in 22 of the 24 included studies, which raises concerns about the reliability of the results.

• Future studies should look at long-term results in diverse types of people and be independent of liraglutide manufacturers.

What is obesity?

Obesity is a long-term condition in which a person has too much body fat. It can increase the risk of health problems like type 2 diabetes, diseases of the heart and blood vessels (cardiovascular disease), and some types of cancer. Obesity levels are increasing worldwide, placing a significant burden on healthcare systems. Managing obesity usually involves lifestyle changes such as eating a healthier diet and being more physically active. However, many people find these changes difficult to maintain, and doctors may prescribe medications to support weight loss.

What is liraglutide?

Liraglutide is a type of medication that helps people feel full sooner, and so eat less. It was originally developed to treat type 2 diabetes but has been approved in many countries to help people lose weight. It is given as a daily injection. Some people taking liraglutide experience unwanted effects, such as feeling or being sick, diarrhoea and constipation. Liraglutide is a ‘GLP-1 receptor agonist’ (GLP-1RA). Similar medications include semaglutide and tirzepatide.

What did we want to find out?

We wanted to know how well liraglutide works in adults with obesity in the medium term (6 to 24 months) and long term (24 months or more). We examined its effects on weight, unwanted effects, obesity-related health problems, quality of life and risk of death. We did not look at what happens after people stop taking liraglutide.

What did we do?

We searched for studies that investigated liraglutide for adults living with obesity. Studies could investigate any dose of liraglutide compared with placebo (sham medication), no treatment, lifestyle changes or another weight-loss medication. We included studies in which people took liraglutide for at least 6 months. We compared and analysed the results and assessed our confidence in the evidence.

What did we find?

We found 24 studies with 9937 men and women with obesity, aged between 31 and 64 years. Some people had weight-related conditions like diabetes or liver disease. Most studies compared liraglutide with placebo. They mainly took place in high- and middle-income countries.

Liraglutide compared to placebo

• Weight loss: people who took liraglutide were more likely to lose at least 5% of their body weight than those who took a placebo in the medium (18 studies, 6651 people) and long term (2 studies, 1262 people). However, we are uncertain about liraglutide’s effects on people’s overall percentage weight change from the beginning of the study to the medium term (16 studies, 6050 people) and there may be little to no difference in percentage weight change in the long term (2 studies, 1262 people).

• Unwanted effects: in the medium term, people taking liraglutide might experience more unwanted effects of any kind (16 studies, 8147 people) and more serious unwanted effects (20 studies, 8487 people) than those taking placebo. We are unsure about mild-to-moderate unwanted effects (17 studies, 7440 people) or whether unwanted effects caused people to stop treatment (19 studies, 8628 people). In the long term (2 studies, 2640 participants), liraglutide may increase unwanted effects and people may be more likely to stop treatment because of them. We are unsure about unwanted events overall and mild-to-moderate unwanted effects.

• Quality of life: liraglutide probably makes little or no difference to quality of life both in the medium term (6 studies, 3733 people) and in the long term (1 study, 863 people)

• Other results: liraglutide probably makes little or no difference to major cardiovascular events in the medium term (6 studies, 5762 people). We are unsure about its effects on major cardiovascular events in the long term and on deaths in the medium and long term.

What are the limitations of the evidence?

We are moderately confident that people taking liraglutide lose more weight than those taking placebo. However, our confidence in the other evidence is limited because of how the studies were conducted and information that was missing. Few studies looked at long-term effects or included different people from different places, so the results may not apply to everyone. The manufacturers of liraglutide were involved in the design, conduct or analysis of 22 of the 24 studies, which limits our confidence in the results. More independent studies are needed.

How up to date is this evidence?

The evidence is up to date to December 2024.