Ozempic, Wegovy, Mounjaro: what the latest scientific studies really say 🔬

You hear about it everywhere: in the office, on the networks, in the gym locker rooms. GLP-1 drugs (Ozempic, Wegovy, Mounjaro, Zepbound...) have changed the game for weight loss. But what do the most recent studies really say about their risks? Here is a factual overview, without sensationalism.

What is it, concretely?

GLP-1 (semaglutide, tirzepatide, liraglutide) imitate a natural hormone that regulates appetite, satiety and gastric emptying. Result: less hunger, fewer calories ingested, and often spectacular weight loss - 15 to 20% of the initial weight in 12 to 24 months according to clinical studies.

The overall benefit/risk ratio remains considered favorable by the health authorities when these treatments are used within their indication framework (diabetes, obesity). But several effects deserve to be known, especially if you accompany clients who are starting or considering this type of treatment.

1. Muscle wasting: the real subject that concerns us 💪🏻

This is THE point that must hold your attention as a coach. Several studies converge: 25 to 40% of the weight lost under GLP-1 comes from lean mass, not just fat. The STEP-1 study on semaglutide had already pointed out this phenomenon, since confirmed by work published in The Lancet Regional Health and Cell.

The good news? It's not inevitable. More recent work (including a series of cases published at the end of 2025) shows that the combination of high protein intake (1.2 to 1.7 g/kg/day) + resistance training 2 to 3 times/week can drop this muscle loss to about 3% of the weight lost - compared to 13% without these measures. In other words: muscle loss is not intrinsic to the drug, it is intrinsic to a poorly accompanied caloric deficit. This is exactly where a coach has a role to play.

2. Digestive effects and emergency room visits

The most documented point remains digestive disorders (nausea, vomiting, diarrhea, abdominal pain, constipation). A study published in April in the Annals of Internal Medicine, based on surveillance data from the US CDC, identified nearly 25,000 semaglutide-related emergency room visits over 2022-2023, mostly for gastrointestinal complications.

3. Bones and joints: a signal to watch out for

Presented in March 2026 at the Congress of the American Academy of Orthopaedic Surgeons, an analysis of more than 146,000 patients showed a relative increase of about 30% in the risk of osteoporosis in GLP-1 users, as well as an increased risk of gout. The researchers themselves call for caution: the signal is real but moderate, and further studies are needed to identify the most exposed populations (especially elderly patients).

4. An unexpected side effect: hair loss

A study of 12,000 patients, widely reported in the medical press in recent days, revealed an increase in the risk of alopecia in GLP-1 users (up to +68% according to some data). The exact mechanism has not yet been clarified, but the most likely hypothesis remains physiological stress related to rapid weight loss and possible deficiencies.

5. Nutritional deficiencies

The French Medicines Agency (ANSM), after two years of pharmacovigilance, calls for vigilance on a point that is still undervalued: nutritional deficiencies (anemia in particular) linked to too rapid weight loss and a spontaneous decrease in food intake.

6. And after stopping treatment? The real moment of truth

This is probably the most underestimated point, and yet the most decisive for your customers. A British study published in early 2026 in the BMJ, on 37 trials devoted to the discontinuation of weight loss treatments, shows that weight regaining after discontinuation of a GLP-1 is about four times faster than after a simple food and sports program. On average, patients lose 15 kg during treatment and regain nearly 10 in one year — with a projection towards a return to the initial weight in 18 months. An older trial went in the same direction: two-thirds of the weight lost was recovered a year after the judgment.

Why? The drug acts on the hormonal mechanisms of hunger and satiety. As soon as it fades in the body, the appetite returns to its pre-treatment level - and if nothing else has changed in the meantime, the body simply resumes the path it knew.

Important nuance: a more recent study by the Cleveland Clinic, published in Diabetes, Obesity and Metabolism, shows that weight gain is not systematic in real life. The patients who do best are those who have built up something else during treatment - new eating habits, installed sports practice - or who continue support after stopping.

This is exactly where the role of the coach plays. A GLP-1 treatment without accompaniment is a weight loss window that closes as soon as the injection is stopped. The drug treats the symptom (excess weight) while it is active, but it does not build anything by itself: neither muscle mass, nor lasting eating habits, nor a healthy relationship to effort. If this substantive work has not been done from the beginning of the treatment - and not only at its cessation - all the effort and money invested may evaporate in 12 to 18 months.

Concretely, the coach has a role to play in three moments:

At the start: set a nutritional framework and a muscle strengthening program while appetite is reduced - this is the ideal time to establish good habits without fighting hunger.

During treatment: follow the body composition to ensure that the loss comes from the fat mass and not from the muscle, adjust the training as the weight decreases.

At a standstill: this is the most risky moment. Appetite gradually rises over several weeks - a tight accompaniment at this time makes it possible to consolidate habits rather than seeing them collapse with the return of hunger.

A customer who arrives with a GLP-1 prescription should not be seen as someone who "no longer needs a coach" - it's the opposite. This is the time when support is most valuable, because it is he who decides whether the results will be temporary or final.

What to remember

✅ The benefit/risk ratio remains favorable for validated medical indications (diabetes, obesity). ⚠️ Muscle loss is the most relevant risk for your sports customers - and the most controllable. ⚠️ Deficiencies, digestive disorders and bone risk justify close medical follow-up, not self-medication. ⚠️ Without a lasting change in habits, weight regaining after stopping is almost systematic - and fast. 🎯 The role of the coach has never been clearer: sufficient protein, regular muscle strengthening, monitoring of body composition, and support that begins from the first day of treatment - not only when it stops. This is what makes the difference between "losing weight" and "permanently changing body".

This article is a general information content and does not replace medical advice. Any treatment decision must be made with a health professional.