Ozempic Is Everywhere. But Do You Actually Know What It Does?

It started as a diabetes medication. Now it is on waiting lists, in headlines, and in the conversation at almost every dinner party. Semaglutide - sold under brand names including Ozempic and Wegovy - has become the most talked-about drug in a generation. But the science behind it is considerably more interesting, and more nuanced, than most of the conversation acknowledges.

What's going on?

GLP-1, or glucagon-like peptide-1, is a hormone your body produces naturally in the gut after eating. Its job is to signal to the brain that food has arrived - triggering insulin release, slowing gastric emptying, and reducing appetite. GLP-1 receptor agonists are synthetic versions of this hormone, engineered to stay active in the body far longer than the natural version, which breaks down within minutes. Semaglutide, the most widely prescribed, produces average weight loss of around 15-17% of body weight over 68 weeks - a figure that approaches results previously only achievable through bariatric surgery (Moiz et al., 2025). For context, the most effective lifestyle interventions typically produce 5-10%. The scale of effect is genuinely unprecedented in the history of obesity pharmacology.

Why is this happening?

What makes GLP-1 receptor agonists so effective is where they act. Their primary mechanism is not in the stomach - it is in the brain. GLP-1 receptors are expressed throughout the hypothalamus and brainstem, the regions that govern appetite, satiety and reward-driven eating behaviour. When activated pharmacologically, these receptors reduce the perceived reward value of food, dampen hunger signals, and slow gastric emptying - together producing a sustained reduction in calorie intake that does not rely on willpower or conscious restriction (Wang et al., 2023). For many users, the experience is a fundamental shift in their relationship with food: the constant background noise of appetite simply quietens.

The cardiovascular evidence is equally compelling. The SELECT trial found that semaglutide meaningfully reduced rates of major cardiovascular events in people with obesity, independently of weight loss alone - suggesting anti-inflammatory and vascular protective effects beyond appetite suppression (Moiz et al., 2025).

What the conversation is missing

There are several limitations that deserve honest attention, and muscle loss is one of the most clinically significant. In the STEP-1 trial, approximately 25-40% of weight lost on semaglutide was lean mass rather than fat tissue (Neeland et al., 2024). This is not unique to GLP-1 drugs - all meaningful caloric restriction involves some loss of lean tissue - but the scale of weight loss these medications produce means the absolute amount of muscle lost can be substantial, particularly in older adults where muscle mass is already declining with age. Loss of skeletal muscle carries consequences for metabolic rate, physical function, insulin sensitivity and long-term health that are entirely separate from the benefits of fat loss.

The practical response is clear and evidence-supported: resistance training combined with adequate protein intake - around 1.2-1.6g per kilogram of body weight per day - can reduce lean mass loss by 40-50% compared to medication alone (Neeland et al., 2024). For anyone on or considering GLP-1 therapy, this is not optional lifestyle advice. It is a clinically important part of using these medications well.

Two further limitations are worth noting. Around 10-15% of users lose little or no weight on semaglutide, and the reasons remain poorly understood. Weight regain after stopping treatment is also well documented - in the STEP 4 trial, participants who discontinued semaglutide regained approximately two thirds of their lost weight within a year (Rubino et al., 2021). This reflects the biology of obesity as a chronic, relapsing condition, not a failure of the drug. But it does mean that for most people, GLP-1 therapy is not a course of treatment. It is an ongoing one.

References:

Moiz, A., Filion, K. B., Tsoukas, M. A., & Eisenberg, M. J. (2025). Mechanisms of GLP-1 receptor agonist-induced weight loss: A review of central and peripheral pathways in appetite and energy regulation. American Journal of Medicine, 138(6), 934-940. 

Neeland, I. J., Linge, J., & Birkenfeld, A. L. (2024). Changes in lean body mass with glucagon-like peptide-1-based therapies and mitigation strategies. Diabetes, Obesity and Metabolism, 26(Suppl 4), 16-27. 

Rubino, D., Abrahamsson, N., Davies, M., Hesse, D., Greenway, F. L., Jensen, C., Lingvay, I., Mosenzon, O., Rosenstock, J., Rubio, M. A., Rudofsky, G., Tadayon, S., Wadden, T. A., & Dicker, D. (2021). Effect of continued weekly subcutaneous semaglutide vs placebo on weight loss maintenance in adults with overweight or obesity: The STEP 4 randomized clinical trial. JAMA, 325(14), 1414-1425. 

Wang, J. Y., Wang, Q. W., Yang, X. Y., Yang, W., Li, D. R., Jin, J. Y., Zhang, H. C., & Zhang, X. F. (2023). GLP-1 receptor agonists for the treatment of obesity: Role as a promising approach. Frontiers in Endocrinology, 14, Article 1085799.