You have probably heard the terms Wegovy, Mounjaro, Ozempic, and GLP-1 thrown around. But what do they actually mean? And how do these medications actually cause weight loss? This guide explains everything from the biology to the practicalities — in plain English.
What Does GLP-1 Stand For?
GLP-1 stands for glucagon-like peptide-1 — a hormone your body naturally produces in the gut after you eat. It plays several important roles:
- Signals fullness to the brain — telling you to stop eating
- Slows gastric emptying — food stays in your stomach longer, extending the feeling of fullness
- Stimulates insulin release — helps regulate blood sugar after meals
- Reduces glucagon — a hormone that would otherwise raise blood sugar
In people with obesity, the body's GLP-1 signalling is often blunted — meaning the fullness signal is weaker, and hunger is harder to control.
How Do GLP-1 Medications Work?
GLP-1 medications are synthetic copies of the natural GLP-1 hormone that are chemically modified to last much longer in the body. Natural GLP-1 breaks down within minutes. The medications last days to weeks, providing a sustained appetite-suppressive effect.
When you inject a GLP-1 medication like Wegovy (semaglutide) or Saxenda (liraglutide), it:
- Binds to GLP-1 receptors in the brain (specifically the hypothalamus) and dramatically reduces hunger
- Slows the rate at which food empties from your stomach — so you feel full longer
- Reduces cravings for high-calorie foods
- Tells the pancreas to release insulin after meals, helping with blood sugar control
What is the Difference Between GLP-1 and GIP?
Some newer medications — specifically Mounjaro (tirzepatide) — are dual GIP/GLP-1 agonists. They also activate the GIP receptor (glucose-dependent insulinotropic peptide), which further amplifies fat burning and appetite suppression through a separate pathway.
Think of GLP-1 as one brake on your appetite, and GIP as a second brake operating independently. Activating both gives stronger, more sustained results — which is why Mounjaro produces greater average weight loss than Wegovy in head-to-head trials.
What Are the Main GLP-1 Medications Available in the UK?
| Medication | Active compound | Injection frequency | MHRA approved for weight loss? | |------------|----------------|---------------------|---------------------------------| | Wegovy | Semaglutide 2.4mg | Weekly | Yes | | Mounjaro | Tirzepatide | Weekly | Yes | | Saxenda | Liraglutide 3mg | Daily | Yes | | Ozempic | Semaglutide 0.5/1/2mg | Weekly | No (licensed for type 2 diabetes) |
Important: Ozempic is frequently discussed in the media as a weight loss drug, but it is only MHRA-licensed for type 2 diabetes in the UK. Using it for weight loss is off-label. Wegovy contains the same active ingredient (semaglutide) at a higher dose and is the MHRA-approved weight loss formulation.
Who Are GLP-1 Medications For?
In the UK, GLP-1 medications for weight loss are licensed for adults with:
- A BMI of 30 or above, or
- A BMI of 27 or above with at least one weight-related health condition (type 2 diabetes, high blood pressure, sleep apnoea, high cholesterol, etc.)
How Are They Taken?
All three main GLP-1 medications available in the UK are self-administered subcutaneous injections — injected into the fatty tissue beneath the skin on your abdomen, thigh, or upper arm. The injection pens are small, pre-filled, and virtually painless. Most patients describe it as much easier than they expected.
Are GLP-1 Medications Safe?
Yes — when prescribed by a registered UK prescriber and taken correctly. All three medications listed above are MHRA-approved for weight loss in the UK. They have been through extensive clinical trials involving tens of thousands of patients.
Common side effects are mainly gastrointestinal (nausea, constipation, diarrhoea) and typically resolve within 4–8 weeks.
Where Can You Get GLP-1 Medication in the UK?
You need a prescription from a GMC-registered prescriber. Options include:
- NHS Specialist Weight Management Services (long waiting lists)
- Private GPhC-registered online pharmacies — fastest route, can start within 48 hours
- Private GP clinics — face-to-face with full medical oversight
The GLP-1 Directory compares all verified UK providers for Mounjaro, Wegovy, and Saxenda — with pricing, patient reviews, and GPhC verification.