Anti-obesity treatments: the most effective have the most side effects

Summary based on an article by Sciences et Avenir with AFP (9 July 2026), reporting a large meta-analysis published in the BMJ.

Summary

The GLP-1 anti-obesity treatments that are most effective at promoting weight loss are also those that cause the most adverse effects, according to a large review published in the BMJ (British Medical Journal), one of the most prestigious medical journals.

Moreover, these medications as a whole have little proven effect on quality of life. "The greatest benefits are generally associated with more adverse effects, more constraints for patients and more discontinuations," conclude the authors, whose work is based on more than 200 studies.

What does this BMJ review show?

GLP-1 treatments, initially developed against diabetes, are now used to promote weight loss, an indication in which they have shown unrivalled efficacy.

The work published in the BMJ aims to compare these treatments, their efficacy and their drawbacks, first and foremost unpleasant side effects, often digestive disorders such as nausea and vomiting.

The most effective treatments

The study shows that the most effective GLP-1 treatments are tirzepatide, marketed under the name Mounjaro by the pharmaceutical group Eli Lilly, and CagriSema, a drug being developed by its competitor Novo Nordisk, which combines the GLP-1 molecule semaglutide with another active ingredient, cagrilintide.

With these two treatments, weight loss is of the order of 15%. For semaglutide alone, marketed under the Wegovy brand, weight loss is only about 10%.

Semaglutide and cardiovascular risk

On the other hand, semaglutide alone is, along with tirzepatide, one of the few GLP-1s to show truly convincing results in reducing cardiovascular risks — a point on which this family of treatments is nonetheless widely considered promising.

Sometimes heavy side effects

More generally, as experts seek to assess to what extent the benefits of GLP-1s justify sometimes heavy side effects, none of these medications has, according to this work, demonstrated that it improves patients' overall quality of life. The hindsight in this area remains limited, and the authors call for longer-term studies.

A challenge for health authorities

"This study represents an important step," praised, in an independent commentary also published in the BMJ, two American obesity experts, Hamlet Gasoyan and Michael B. Rothberg, stressing that it allowed patients and doctors to better compare treatment options in a rapidly evolving field.

The challenge is also important for health authorities, which must decide the level of reimbursement of these treatments, all of which are quite costly. France has just authorised the reimbursement of Wegovy and Mounjaro, but according to strict criteria that exclude many patients.

The Valorian analysis

This review illustrates a fundamental principle of evidence-based medicine: the efficacy of a treatment must always be weighed against its adverse effects, its constraints and its real impact on quality of life. GLP-1 treatments represent a major advance in the management of obesity, but they are neither a universal solution nor a substitute for the fundamentals: balanced diet, physical activity, sleep and medical follow-up.

At Valorian, we consider that these medications, when indicated, must be part of a comprehensive and personalised strategy, with rigorous medical support, an assessment of the expected benefits (weight loss, reduction of cardiovascular risk) and monitoring of adverse effects. The decision to treat, to choose a molecule and to continue its use is a matter for an informed dialogue between the patient and their doctor, and not a fashion.