Define GLP-1: What It Is and How GLP-1 Medicines Work

01 · Definition

What does GLP-1 mean?

GLP-1 stands for glucagon-like peptide-1, a hormone released by the gut after eating. It signals the brain and digestive system that food has arrived. In practice, higher GLP-1 activity means you feel fuller sooner and less hungry between meals.¹

The term is also shorthand for GLP-1 receptor agonists, the medicines that activate those same receptors. You may see them called GLP-1s, GLP-1 injections or weight-loss jabs.

02 · Next step

Is a GLP-1 medicine relevant to you?

It may be if you are an adult seeking medically supported weight management, or you have type 2 diabetes. Treatment is prescription-only and used alongside a reduced-calorie diet and increased physical activity.¹

If you want to explore it, our weight loss clinic explains the process. The Mounjaro pen starts at £169.99 for the 2.5mg starting pen, and new customers save £40 on their first order with code FIRST40. A free consultation is reviewed by a GPhC-registered prescriber.

Related guides: Define mounjaro and Boehringer ingelheim glp 1 and Agonisti glp 1 and Wat is glp-1 and Ozempil glp-1.

03 · How GLP-1 medicines work

How GLP-1 medicines work

GLP-1 medicines regulate appetite, slow how quickly the stomach empties, and improve the way the body responds to insulin.¹ The practical effect is feeling fuller sooner, which supports a reduced-calorie diet.

Semaglutide (Wegovy, Ozempic) is a single-action GLP-1 medicine. Tirzepatide is the first treatment of its kind to activate two natural gut-hormone receptors at once: GIP and GLP-1. That dual action is what distinguishes Mounjaro from single-action medicines.¹

In the SURMOUNT-1 trial of 2,539 adults, people taking tirzepatide alongside diet and exercise lost on average 15% of their body weight on 5mg, 19.5% on 10mg and 20.9% on 15mg over 72 weeks, compared with 3.1% with lifestyle changes alone.² These are trial averages and individual results vary.

04 · Types of GLP-1 medicine

Types of GLP-1 medicine

GLP-1 medicines differ in schedule and in how many hormone receptors they target. Mounjaro and Wegovy are once-weekly pens, while liraglutide (Saxenda) is a daily injection.¹⁸

Wegovy follows a dose ladder of 0.25mg, 0.5mg, 1mg, 1.7mg and 2.4mg, stepping up after 4 weeks on each of the first four doses, so the 2.4mg maintenance dose starts from week 17. Mounjaro comes as a multi-dose KwikPen in strengths from 2.5mg to 15mg.¹ You can compare the Wegovy pen with Mounjaro.

Tablet forms such as Wegovy tablets and Foundayo also exist.

05 · Safety and who should check first

Safety and who should check first

A GLP-1 medicine is only suitable after a prescriber has reviewed your health history. Your prescriber will take extra care, or may recommend against treatment, if you have a history of pancreatitis, severe gut or digestive disease, diabetic retinopathy, or gallbladder problems.

Two interactions are worth knowing. Because Mounjaro slows stomach emptying, it can reduce how well oral contraceptive pills are absorbed.⁷ The SmPC advises switching to a non-oral method, or adding a barrier method (such as condoms), for 4 weeks after starting Mounjaro and for 4 weeks after each dose increase.¹ If you use insulin or sulfonylureas, doses may need adjusting because of the risk of low blood sugar. Tell your prescriber about every medicine you take.

Serious side effects are uncommon but need urgent attention. Seek immediate medical help for severe, persistent stomach pain that may spread to your back, with or without vomiting (possible pancreatitis); pain in the upper right abdomen, fever or yellowing of the skin or eyes (possible gallbladder problems); or signs of a severe allergic reaction such as swelling of the face or throat and difficulty breathing. For any other new or worrying symptom, speak to your prescriber and report it through the Yellow Card scheme.¹⁹

06 · NHS and private access

NHS and private access

Mounjaro is available on the NHS, but access is being phased in over several years. NICE recommends it for adults with a BMI of at least 35 plus at least one weight-related condition, and the NHS primary-care rollout began in June 2025 with the highest-need groups first.⁴⁶

Full rollout is expected to take years, which is why many people who meet the licensed criteria choose regulated private treatment. Our service is a GPhC-registered pharmacy (9012878) with official LillyDirect supply and free next-day tracked delivery.