GLP-1: the hormone under it all
GLP-1 (glucagon-like peptide-1) is released by your gut within minutes of eating. It does three jobs: tells your brain's appetite centres that food has arrived, slows the rate your stomach empties (so fullness lasts), and prompts glucose-dependent insulin release. It is your body's own portion-control system, and in people living with obesity, that signalling often underperforms.
GLP-1 medicines are synthetic versions engineered to last. Natural GLP-1 breaks down in minutes; the medicines survive days, which is why they can be taken weekly (or once daily, in tablet form).
The family, mapped
| Product | Drug | Target(s) | UK licence |
|---|---|---|---|
| Mounjaro | Tirzepatide | GIP + GLP-1 (dual) | Type 2 diabetes; weight management |
| Wegovy | Semaglutide | GLP-1 | Weight management (injection up to 2.4 mg; 7.2 mg approved Jan 2026) |
| Wegovy pill | Oral semaglutide | GLP-1 | Weight management. Approved June 2026 |
| Ozempic | Semaglutide | GLP-1 | Type 2 diabetes only |
| Rybelsus | Oral semaglutide | GLP-1 | Type 2 diabetes only |
| Saxenda | Liraglutide | GLP-1 (daily injection) | Weight management (older generation) |
The mental shortcut: same hormone, different packages. Tirzepatide adds a second hormone target (GIP) which appears to be why it produces the largest average weight losses (up to ~21% in SURMOUNT-1). Everything else follows from the licence: weight management or diabetes, injection or tablet.
What being on one actually feels like
People describe it remarkably consistently: food gets quieter. Portions shrink naturally because fullness arrives early and stays. "Food noise" (the background hum of thinking about eating) fades for most users. Side effects (mostly gastrointestinal) cluster in the early weeks and after dose increases; our side effects guide separates normal from red-flag.
What they do not do: melt fat directly, replace protein and training (muscle loss is the trap of passive use. See the protein calculator), or work identically for everyone. Response varies genuinely and unpredictably.
Who they are for in the UK
For weight management, the licensed population is adults with obesity (BMI ≥30) or overweight (BMI ≥27 to 30) with a weight-related condition, alongside diet and activity changes. NHS access is narrower. NICE thresholds of BMI ≥35 plus a comorbidity (TA875 for semaglutide, TA1026 for tirzepatide), with lower thresholds for some ethnic backgrounds, and phased rollout through specialist services and, for tirzepatide, primary care. Private access via GPhC-registered pharmacies is how most UK patients currently start.
They are not for cosmetic weight loss in people at healthy weights, not for pregnancy, and require caution with pancreatitis history, certain thyroid cancer family history, and severe gastrointestinal disease.
The long game
These are chronic-condition medicines, not courses. Weight regain after stopping is the statistical norm. In the withdrawal trials, two-thirds of the lost weight returned within a year. That is why the smart framing is simple: the medication is scaffolding, and the habits (protein, training, structure, sleep) are the building. This philosophy sits behind every guide on this site, from nutrition to maintenance.
Frequently asked questions
What does GLP-1 stand for? +
Glucagon-like peptide-1. A hormone your gut releases after eating that signals fullness to the brain, slows stomach emptying and supports blood-sugar control. GLP-1 medicines are long-acting synthetic versions of it.
What is the difference between GLP-1 medicines? +
The drug (semaglutide vs tirzepatide. The latter also targets GIP), the licence (weight management vs type 2 diabetes), the format (weekly injection or daily tablet) and the dose. Same hormone family, different packages.
Are GLP-1 medicines insulin? +
No. They prompt your body to release insulin only when blood sugar is high, which is why they rarely cause low blood sugar on their own. They are peptide hormone mimics, not insulin replacements.
How fast do GLP-1 medicines work? +
Appetite effects are often felt in the first week or two. Meaningful weight change typically appears over 8 to 12 weeks as doses titrate up. The big trial numbers people quote (15 to 21%) are results over 16 to 18 months.
Are GLP-1 medicines safe long-term? +
The major trials now run multiple years with reassuring overall profiles, and these medicines have been used in diabetes since 2005 (liraglutide) and 2017 (semaglutide). Known serious risks (pancreatitis, gallbladder disease, rare NAION with semaglutide) are monitored by the MHRA, and long-term surveillance continues.
References & official sources
Show all 5 cited sources, with study authors +
- NICE NG246. Overweight and obesity management: www.nice.org.uk/guidance/ng246
- NICE TA1026. Tirzepatide for managing overweight and obesity: www.nice.org.uk/guidance/ta1026
- NICE TA875. Semaglutide for managing overweight and obesity: www.nice.org.uk/guidance/ta875
- NHS. Obesity: treatment: www.nhs.uk/conditions/obesity/treatment/
- Jastreboff AM et al. Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1). NEJM 2022: www.nejm.org/doi/full/10.1056/NEJMoa2206038