Semaglutide / GLP-1 agonists
Also known as: ozempic, wegovy, tirzepatide, mounjaro
Licensed prescription medicines with strong trial evidence: included here because they are misused outside that, not because they belong with the rest.
Legal status: UK: prescription-only medicine; legitimately available only via a doctor's prescription. Checked 2026-07-26.
Prohibited in sport: See WADA.
Approved medical use: Licensed for type-2 diabetes and, for some formulations, for weight management in people meeting specified criteria.
What it is
GLP-1 receptor agonists mimic a gut hormone released after eating. They slow gastric emptying, improve insulin response and act on appetite centres in the brain, substantially reducing hunger. Unlike most compounds in this library these are licensed, well-studied medicines with large outcome trials behind them.
They are prescribed for type-2 diabetes and, for specific formulations, for weight management in people meeting defined clinical criteria, with dose titration, side-effect management and follow-up all part of the treatment.
What’s claimed
- Large, sustained weight loss
- Effortless appetite control
- A shortcut to contest or holiday leanness
What the evidence shows
The weight-loss and cardiometabolic effects are well-supported by large randomised trials (Gold): this is among the strongest evidence bases in the whole library. The problem the library exists to address is the gap between that evidence and how these drugs are being used in fitness culture: bought outside a prescription, used by people who are already lean, and used without the muscle-preserving protein and resistance training that the clinical guidance is explicit about. A meaningful fraction of the weight lost is lean mass when that is neglected.
The risks
- Gastrointestinal: nausea, vomiting, constipation and diarrhoea are common, and severe dehydration from persistent vomiting is a recognised cause of hospital admission.
- Pancreatitis and gallbladder disease are recognised, if uncommon, complications.
- Lean mass loss where protein intake and resistance training are inadequate: the specific risk for people using these in a fitness context.
- Counterfeits: the supply shortage produced a large illegitimate market, and counterfeit pens containing insulin instead have caused serious harm including hospitalisation.
- Not for everyone: they are contraindicated in pregnancy and in certain thyroid and pancreatic histories, which is exactly what a prescribing consultation is for.
What needs monitoring
- Weight and body composition, not weight alone
- Blood glucose and HbA1c where diabetes is involved
- Hydration and gastrointestinal tolerance
- These are prescription medicines: the monitoring is the prescriber's job, and obtaining them outside that removes it.