What Are GLP-1 Medications? A Plain-English Guide

GLP-1 medications are prescription medicines that copy the action of a natural gut hormone called glucagon-like peptide-1. They reduce appetite, help you feel full sooner and slow the rate at which the stomach empties, and they help control blood glucose. In the UK they are used to treat type 2 diabetes and, for some medicines, to manage weight. Examples include Wegovy (semaglutide), Mounjaro (tirzepatide, which also acts on a second hormone, GIP), Saxenda (liraglutide) and two newly licensed tablets. All are prescription-only, and whether one suits you is a decision for a prescriber.

What is GLP-1?

GLP-1 stands for glucagon-like peptide-1. It is a hormone made by specialised cells in the lining of the small intestine and released into the bloodstream when you eat. A "peptide" is a short chain of amino acids, the building blocks of proteins.

Natural GLP-1 has several jobs:

• It boosts insulin release from the pancreas when blood glucose is high. Importantly, this effect depends on glucose levels, so it does little when glucose is normal or low.
• It reduces glucagon, a hormone that raises blood glucose.
• It slows stomach emptying, so food leaves the stomach more gradually.
• It acts on the brain to increase feelings of fullness and reduce hunger.

The natural hormone is broken down within a couple of minutes by an enzyme called DPP-4. That makes it unsuitable as a medicine in its own right. GLP-1 medicines are designed to resist this breakdown, so their effects last for a day or a week, depending on the medicine.

How GLP-1 medicines work

GLP-1 medicines are known as GLP-1 receptor agonists. A receptor is like a lock on the surface of a cell; an agonist is a key that turns it. These medicines bind to the same receptors as natural GLP-1 and switch on the same signals.

Appetite and the brain

The main way GLP-1 medicines produce weight loss is through the brain. GLP-1 receptors are found in areas of the brain that regulate hunger, fullness and the reward value of food. People taking these medicines commonly report:

• feeling full sooner and for longer
• less hunger between meals
• fewer cravings and less preoccupation with food, sometimes described as quieter "food noise"

Eating less, more comfortably, leads to weight loss over time.

The stomach

Slower stomach emptying contributes to fullness, particularly early in treatment. It is also the reason for some side effects, such as nausea, bloating and reflux, and it matters for anaesthesia. Our guide to GLP-1 medication before surgery explains why.

Blood glucose

By increasing insulin release when glucose is high and reducing glucagon, GLP-1 medicines lower blood glucose. That is why they were first developed for type 2 diabetes. Because the insulin effect depends on glucose levels, they rarely cause hypoglycaemia on their own, although the risk rises when combined with insulin or sulfonylureas.

Dual and newer agonists

Some newer medicines act on more than one hormone receptor:

• Tirzepatide (Mounjaro) acts on both GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 receptors. GIP is another gut hormone involved in insulin release and fat metabolism. Our guide to how Mounjaro works explains the dual mechanism.
• Orforglipron (Foundayo) is a GLP-1 receptor agonist, but unlike the others it is not a peptide. It is a small molecule, which means it can be absorbed from a tablet without the strict fasting rules needed for oral semaglutide.
• Medicines in development act on further hormones such as glucagon and amylin. See our guide to the GLP-1 pipeline.

A brief history

GLP-1 research goes back to the 1980s. The first GLP-1 medicine for type 2 diabetes, exenatide, was derived from a substance found in the saliva of the Gila monster lizard and was approved in Europe in 2006. Liraglutide followed for diabetes (Victoza) and later, at a higher dose, for weight management (Saxenda).

Semaglutide was developed as a once-weekly injection for diabetes (Ozempic) and later at a higher dose for weight management (Wegovy), which the MHRA authorised in 2021. Tirzepatide was authorised for type 2 diabetes and then, in the UK, for weight management in late 2023.

In 2026, the MHRA approved the first GLP-1 tablets for weight management in the UK: oral semaglutide (Wegovy tablets) in June and orforglipron (Foundayo) in August. The MHRA also approved a higher 7.2mg maintenance dose of Wegovy for some adults with obesity in January 2026.

GLP-1 medicines available in the UK

Licences and availability change, so check the current SmPC on medicines.org.uk or ask a pharmacist. Our overview of every weight loss medication available in the UK also covers non-GLP-1 options such as orlistat.

Why Ozempic is not the same as Wegovy

Ozempic and Wegovy contain the same active ingredient, semaglutide, but they are different products with different licences, doses and pens. Ozempic is licensed for type 2 diabetes. Wegovy is licensed for weight management at higher doses. Our guide to Ozempic vs Wegovy explains why the distinction matters, including for supply to people with diabetes.

What the evidence shows

Weight loss

Large randomised trials have tested GLP-1 medicines in adults with obesity or overweight, alongside lifestyle advice:

These are averages. Some people lose considerably more, and some lose much less or very little. Trials took place under close supervision with lifestyle support, which may differ from everyday practice. Comparisons between trials should be made cautiously because populations and designs differ. Our guide to realistic weight loss expectations discusses this.

Beyond weight

• Heart health: the SELECT trial found semaglutide 2.4mg reduced the risk of major cardiovascular events in people with overweight or obesity and established cardiovascular disease, without diabetes. See our guide to Wegovy and the SELECT trial.
• Sleep apnoea: the SURMOUNT-OSA trials found tirzepatide reduced the severity of obstructive sleep apnoea in adults with obesity. See our guide to tirzepatide and sleep apnoea.
• Type 2 diabetes: GLP-1 medicines lower blood glucose and are widely used in diabetes care. See our guide to GLP-1 medication and type 2 diabetes.

Who can use them

For weight management, UK licences for Wegovy and Mounjaro generally cover adults with a BMI of 30 or above, or 27 or above with at least one weight-related condition such as high blood pressure, type 2 diabetes or heart disease. Lower thresholds may be considered for people from some ethnic backgrounds. Treatment is always alongside a reduced-calorie diet and increased physical activity.

Meeting the criteria does not mean treatment is automatically appropriate. A prescriber will consider your medical history, medicines and goals. Our guides to who can get weight loss injections and who should not take GLP-1s explain the details. You can use our BMI calculator or eligibility checker for general information, but neither makes a prescribing decision.

Who should not use them

The SmPCs list reasons not to use these medicines or to use them with caution. Examples include:

• pregnancy, trying to conceive or breastfeeding
• a personal or family history of medullary thyroid carcinoma or multiple endocrine neoplasia type 2 (as noted in the product information)
• previous pancreatitis
• severe gastrointestinal disease, such as gastroparesis
• type 1 diabetes (these medicines are not a substitute for insulin)

How they are taken

Injections

Wegovy and Mounjaro are given once a week using a pre-filled pen, injected under the skin of the abdomen, thigh or upper arm. Saxenda and other liraglutide products are injected daily. Treatment starts at a low dose and increases gradually, usually every four weeks for the weekly injections, to help the body adjust. Our guides to Mounjaro doses and Wegovy doses explain the schedules.

Tablets

Wegovy tablets (oral semaglutide) are taken once daily. Because semaglutide is a peptide that is easily broken down, the tablet must be taken on an empty stomach with only a small sip of water, and you must wait before eating, drinking or taking other medicines. Foundayo (orforglipron) is taken once daily without these restrictions. Our oral GLP-1 guide explains the differences.

Side effects

Common

Most side effects are gastrointestinal and are most noticeable when starting treatment and after each dose increase:

• nausea
• diarrhoea
• constipation
• vomiting
• indigestion, reflux and burping
• abdominal discomfort or bloating
• tiredness and headache
• injection site reactions (for injections)

They are usually mild to moderate and often ease over time. Eating smaller meals, avoiding rich or fatty food, and staying hydrated can help. Our guide to managing nausea on GLP-1 medication has practical tips.

Less common but serious

• Pancreatitis: inflammation of the pancreas, causing severe abdominal pain. Rare but serious.
• Gallbladder problems: including gallstones, more likely with rapid weight loss.
• Dehydration and kidney problems: from vomiting or diarrhoea.
• Hypoglycaemia: mainly when combined with insulin or sulfonylureas.
• Worsening diabetic eye disease: reported with rapid glucose improvement in people with existing retinopathy.
• Allergic reactions: rare.

Other effects people notice

Some people experience hair thinning, usually linked to rapid weight loss, or changes in facial appearance as fat is lost. Muscle mass can fall alongside fat, which is why protein and strength exercise matter. Our guide to preserving muscle on GLP-1 treatment covers this.

What happens when you stop

GLP-1 medicines work while you take them. When they are stopped, appetite tends to return, and trials such as STEP 4 and SURMOUNT-4 found that many participants regained a substantial proportion of the weight they had lost. This does not mean the medicines have failed; it reflects the long-term nature of obesity. Our guides to weight regain after stopping and obesity as a chronic disease explain the evidence.

What treatment is typically like

Everyone's experience is different, but treatment with a weekly GLP-1 injection often follows a broad pattern. The timings below are general and depend on the medicine, dose schedule and individual response.

Your prescriber should review you regularly, particularly at dose changes, and may decide to stay at a lower dose if it is working well or if side effects are a problem. Not everyone needs or tolerates the highest dose. If treatment does not produce meaningful weight loss after a reasonable period, prescribers may consider stopping or changing approach; our guide to what to do if GLP-1 treatment does not work explains the options.

Diet and activity alongside treatment

GLP-1 medicines are licensed for use alongside a reduced-calorie diet and increased physical activity. That is not a formality. Because appetite is reduced, what you eat matters even more:

• Protein at each meal helps protect muscle. See our guide to protein intake.
• Fibre and fluids help prevent constipation.
• Smaller portions and slower eating reduce nausea.
• Rich, fatty or very sugary foods are more likely to trigger side effects for some people.
• Strength exercise two or more times a week, plus regular moderate activity, supports muscle, bone and long-term weight maintenance.

Our guide to what to eat on GLP-1 medication offers practical meal ideas.

What GLP-1 medicines do not do

It is just as useful to understand the limits of these medicines:

• They do not "melt fat". They help you eat less; weight loss comes from the resulting energy deficit.
• They do not work equally for everyone. Some people lose much less weight than trial averages.
• They do not replace diabetes insulin in type 1 diabetes.
• They do not treat the causes of weight gain such as sleep problems, stress, medicines or emotional eating, though they may make eating changes easier.
• They do not keep working after you stop. Benefits generally fade when treatment ends.
• They are not cosmetic treatments. UK licences are based on BMI and health criteria, and prescribing for people below these thresholds is not in line with the licence.

Our guide to GLP-1 myths and facts looks at common misconceptions in more detail, and our 50 common questions answered covers a wide range of practical queries.

Getting a GLP-1 medicine safely

GLP-1 medicines are prescription-only medicines in the UK. They can be prescribed:

• through the NHS, via specialist weight management services (for Wegovy under NICE TA875) or, increasingly, primary care (for Mounjaro under NICE TA1026, in phases)
• privately, through regulated online pharmacies, online doctor services and clinics, after a consultation

The MHRA has repeatedly warned about fake or unlicensed weight loss products sold through social media, beauty salons and unregulated websites. These may contain the wrong dose, the wrong substance or contaminants. Our guide to fake and unlicensed weight loss jabs explains how to recognise warning signs.

Costs for private treatment vary by medicine, dose and provider. We do not list prices in our guides, but our price comparison explains what affects cost, and our provider comparison shows how regulated services differ.

Key terms explained

For related reading, browse our medication guides, or visit our hubs for weight loss injections and oral GLP-1 tablets.

When to speak to a professional

Speak to your GP, a pharmacist or a regulated prescriber if:

• you are wondering whether a GLP-1 medicine might be suitable for you
• you have type 2 diabetes and want to understand your treatment options
• you are pregnant, planning a pregnancy or breastfeeding
• you take other regular medicines, especially insulin, sulfonylureas, warfarin or the contraceptive pill
• side effects are troublesome or not settling

Seek urgent medical help (call NHS 111, or 999 in an emergency) if you are taking a GLP-1 medicine and have:

• severe, persistent abdominal pain, which may spread to your back, with or without vomiting
• pain in the upper right abdomen with fever or yellowing of the skin or eyes
• signs of severe dehydration, such as very little urine, confusion or fainting
• signs of a severe allergic reaction, such as swelling of the face, lips or throat, or difficulty breathing

Suspected side effects can be reported to the MHRA through the Yellow Card scheme.