No drug in recent memory has captured public attention like semaglutide — sold as Ozempic for diabetes and Wegovy for weight loss. The "Abnehmspritze" has become a cultural phenomenon, a dinner-party topic, and a genuine medical breakthrough all at once. But between the hype and the backlash, what does the evidence actually show?

The weight loss data

The STEP trials — the pivotal randomized controlled trials for semaglutide as a weight-loss drug — showed results that were genuinely unprecedented in obesity medicine.

In STEP 1 (n=1,961), participants receiving weekly semaglutide 2.4mg lost an average of 14.9% of their body weight over 68 weeks, compared to 2.4% in the placebo group. About one-third of participants lost 20% or more of their body weight — a magnitude previously seen mainly after bariatric surgery.

These are not modest effects. For a person weighing 100 kg, that's 15 kg of weight loss, sustained over more than a year. At the time, no lifestyle intervention and no previous medication had come close to this in a randomized trial. Since then, tirzepatide, a dual GIP/GLP-1 agonist, has gone further: about 21% average weight loss at the highest dose in SURMOUNT-1.

The cardiovascular data — this is the bigger story

Weight loss drugs have historically struggled with cardiovascular safety. Several have been pulled from the market for causing heart problems. So when the SELECT trial (n=17,604) showed that semaglutide reduced major cardiovascular events by 20% in overweight or obese adults with established cardiovascular disease but without diabetes, it changed the entire conversation.

This is not just a weight loss drug. It's a cardiovascular risk reduction tool. Guidelines have begun to reflect this: the 2024 ESC guidelines on chronic coronary syndromes say semaglutide should be considered in overweight or obese patients without diabetes (class IIa).

14.9%Average weight loss (STEP 1)
20%CV event reduction (SELECT)
17,604Patients in SELECT trial

The side effects — honest accounting

Semaglutide is not a free lunch. The most common side effects are gastrointestinal: nausea (44% in STEP 1, vs 17% with placebo), diarrhea, vomiting, and constipation. These typically improve over weeks as the dose is titrated up, but for some patients they remain significant.

More concerning are the rarer adverse events: pancreatitis (rare but documented), gallbladder disease (weight loss itself is a risk factor), and a potential signal for thyroid C-cell tumors seen in animal studies (relevance to humans uncertain). There are also reports of muscle mass loss alongside fat loss — which is a real clinical concern, especially in older adults where preserving muscle is critical.

The rebound problem

The STEP 1 extension trial showed that patients who stopped semaglutide regained approximately two-thirds of the weight they had lost within one year. This is not a cure for obesity — it's a chronic medication. Patients need to understand this before starting.

Who should consider GLP-1 therapy

Based on current evidence, GLP-1 receptor agonists are most clearly beneficial for:

  • Patients with BMI ≥30 (or ≥27 with weight-related comorbidities) who have not achieved adequate weight loss through lifestyle intervention alone
  • Patients with type 2 diabetes — particularly those with cardiovascular disease or high cardiovascular risk
  • Patients with established cardiovascular disease and overweight or obesity (BMI ≥27) without diabetes — the SELECT population

They are not appropriate for people seeking to lose vanity weight, bodybuilders looking for a shortcut, or anyone with a history of medullary thyroid cancer or MEN2 syndrome.

A reasonable approach

The sensible starting point is not the drug but the metabolic picture. Insulin resistance, prediabetes and metabolic syndrome can be identified with widely available measurements such as HOMA-IR, HbA1c, triglycerides and liver enzymes, together with weight, waist and blood pressure. These findings, plus cardiovascular history, determine whether GLP-1 therapy is worth discussing at all.

If it is, the decision belongs with you and your treating physician — ideally someone experienced with these drugs, such as an endocrinologist, who can manage the titration, monitor side effects, and help preserve muscle mass through concurrent exercise.

Equally, evidence-based practice means not starting it without a clear clinical indication. The cultural pressure to use these drugs for cosmetic weight loss is real — but so are the side effects and the rebound data. A good prescriber recommends the drug when the evidence supports it, and says no when it doesn't.

Questions to ask your doctor

  • Do my BMI, metabolic markers and cardiovascular risk meet the criteria in the trials?
  • How will side effects and muscle mass be monitored during titration?
  • What is the plan if I stop — or if I need to stay on it long term?

References

  1. Wilding JPH, et al. Once-weekly semaglutide in adults with overweight or obesity (STEP 1). N Engl J Med. 2021;384:989-1002.
  2. Lincoff AM, et al. Semaglutide and cardiovascular outcomes in obesity without diabetes (SELECT). N Engl J Med. 2023;389(24):2221-2232.
  3. Wilding JPH, et al. Weight regain and cardiometabolic effects after withdrawal of semaglutide (STEP 1 extension). Diabetes Obes Metab. 2022;24(8):1553-1564.
  4. Jastreboff AM, et al. Tirzepatide once weekly for the treatment of obesity (SURMOUNT-1). N Engl J Med. 2022;387:205-216.
  5. Vrints C, et al. 2024 ESC Guidelines for the management of chronic coronary syndromes. Eur Heart J. 2024;45(36):3415-3537.
Prof. Dr. med. Markus Guba

Head of Liver Surgery and Transplantation at LMU University Hospital Munich. Edits this independent journal in a private capacity; views are his own. About →

This article is general information and not individual medical advice. Decisions about tests and treatment belong in a conversation with your own physician.