8 GLP-1 myths (and what the science says)
Common claims about Ozempic, Mounjaro and Wegovy confronted with published evidence. No scaremongering, no hype: what is known and what is not.
1. "GLP-1s are only for diabetes"
Semaglutide (Wegovy) was approved by the FDA for chronic weight management in 2021; tirzepatide (Zepbound) followed in 2023. Both are indicated for adults with obesity or overweight with at least one related comorbidity, regardless of diabetes status. Wegovy also gained an indication for cardiovascular risk reduction after the SELECT trial (17,604 patients, 20% reduction in major cardiovascular events).
2. "You regain all the weight when you stop"
The STEP 1 extension showed that one year after stopping semaglutide, participants regained roughly two-thirds of the weight lost (net loss went from 17.3% to 5.6%). However, some cardiometabolic improvements (HbA1c, lipids, inflammatory markers) persisted even after partial regain. This confirms that obesity is a chronic disease that may require long-term treatment — just like hypertension — not that the medication "failed".
3. "GLP-1s are dangerous"
The safety analysis of the SELECT trial showed that semaglutide 2.4 mg had fewer serious adverse events than placebo across all BMI categories. The most common side effects are gastrointestinal (nausea, vomiting, diarrhoea, constipation), generally mild to moderate and transient. FDA approval requires Phase III trials with thousands of participants.
4. "You don't need exercise or a healthy diet"
Clinical guidelines are clear: GLP-1s are a complement to healthy eating and physical activity, not a substitute. The Obesity Medicine Association standards (2025) reinforce that pharmacotherapy works best within a comprehensive lifestyle plan.
5. "GLP-1s cause thyroid cancer"
The boxed warning is based on rodent studies where semaglutide caused thyroid C-cell tumours. However, the GLP-1 receptor is not expressed in normal human thyroid tissue. In clinical trials with semaglutide, no cases of medullary thyroid carcinoma or clinically relevant calcitonin changes have been reported. The FDA label itself states: "Human relevance could not be determined." The contraindication remains as a precaution for people with a personal or family history of medullary thyroid carcinoma or MEN2.
6. "It only works if you have a lot of weight to lose"
In 2024, the FDA removed specific BMI thresholds from the indications for semaglutide and tirzepatide. The current indication is for adults with obesity or overweight plus at least one related comorbidity (hypertension, dyslipidaemia, sleep apnoea, cardiovascular disease). The benefit is not limited to severe obesity.
7. "GLP-1s destroy muscle"
Roughly 20–30% of total weight lost is lean mass — a proportion consistent with any weight-loss method (diet, surgery). GLP-1-induced loss is predominantly fat, with a modest absolute decrease in lean mass and no consistent impairment of strength or function. Preclinical data even suggest improvements in muscle quality (mitochondrial efficiency, reduced intramuscular fat). The key: adequate protein (over 1.2 g/kg/day) and resistance exercise.
8. "It's the easy way out"
The AMA recognised obesity as a chronic, relapsing disease in 2013. Evidence-based treatment includes lifestyle intervention, pharmacotherapy and surgery, chosen through shared decision-making between patient and healthcare provider. Calling medication "the easy way out" reflects stigma, not science.
Related guides
- Nausea: what's normal and when to consult — frequency, duration and warning signs.
- What to eat during GLP-1 treatment — nutrition, protein and deficiencies to watch.
- How to use your GLP-1 pen correctly — injection, sites, storage and common mistakes.
Sources: FDA prescribing information for Ozempic (2025), Wegovy (2021), Mounjaro (2022); SELECT trial (NEJM/PMC 2024); STEP 1 extension (PubMed 2022); OMA standards 2025 (PMC); GLP-1 and thyroid review (PMC 2023); lean mass and GLP-1 review (PMC 2025); AMA — recognition of obesity as a disease (2013).