Every UK Weight Loss Injection Compared

Three injectable medicines are licensed for weight management in the UK: Mounjaro (tirzepatide), Wegovy (semaglutide) and Saxenda (liraglutide). Mounjaro and Wegovy are once-weekly injections; Saxenda is injected daily. In clinical trials, tirzepatide has produced the largest average weight loss, followed by semaglutide, then liraglutide, but there is no single "best" weight loss injection for everyone. The right option depends on your health, other medicines, how you tolerate side effects and how you can access treatment, and that decision belongs to a prescriber. This guide sets out how the three compare, using the published evidence.

The three licensed injections at a glance

All three medicines belong to a family often called GLP-1 medicines. They copy, or act on the same receptors as, hormones your gut releases after eating. These hormones signal fullness to the brain, slow the rate at which the stomach empties and help regulate blood sugar. The practical effect for most people is a smaller appetite and fewer food cravings, which makes eating less easier to sustain.

The differences lie in the molecule, how often it is injected, how strong the effect has been in trials and what the licence covers.

Trial figures are averages from different trials with different populations and designs, so they should not be compared too precisely. The one direct comparison, SURMOUNT-5, is covered below.

For a deeper look at each medicine, see our hub pages for Mounjaro and Wegovy, or the overview of all weight loss injections.

Who the injections are licensed for

The licences for all three injections are broadly similar. Each is licensed for adults, used alongside a reduced-calorie diet and increased physical activity, who have:

• a BMI of 30 kg/m² or more (obesity), or
• a BMI of 27 kg/m² up to 30 kg/m² (overweight) with at least one weight-related health condition, such as type 2 diabetes, high blood pressure, abnormal blood fats, obstructive sleep apnoea or cardiovascular disease.

Wegovy and Saxenda also have licences covering some adolescents aged 12 and over, under specialist care. Mounjaro's weight management licence covers adults.

A licence sets the outer limits of who a medicine can be prescribed for. It is not the same as NHS eligibility, which is narrower, and it does not mean a prescriber must offer it. A prescriber also considers things like your medical history, other medicines, previous pancreatitis, a personal or family history of certain thyroid cancers, pregnancy plans and eating disorder history. Our guide to who can get weight loss injections explains this in more detail, and BMI and treatment eligibility covers how the thresholds are applied, including the lower thresholds used for some ethnic groups.

How each injection works

Mounjaro (tirzepatide): a dual-action medicine

Tirzepatide is a single molecule that acts on two hormone receptors: GLP-1 and GIP (glucose-dependent insulinotropic polypeptide). GIP is another gut hormone involved in insulin release and energy balance. Researchers think the combined action is part of why tirzepatide has produced larger average weight loss than GLP-1-only medicines, although the exact contribution of GIP is still being studied.

It is injected once a week under the skin of the tummy, thigh or upper arm. The dose starts at 2.5mg, which is a starter dose to help the body adjust rather than a dose expected to produce much weight loss. It can then be increased in 2.5mg steps, usually no more often than every four weeks, up to a maximum of 15mg. Not everyone needs or tolerates the top dose. See our Mounjaro dosing schedule for detail.

Wegovy (semaglutide): the established weekly option

Semaglutide acts only on the GLP-1 receptor but is designed to last about a week in the body. Wegovy is the weight-management brand; Ozempic, which contains the same ingredient at different doses, is licensed in the UK for type 2 diabetes only.

Wegovy starts at 0.25mg weekly and steps up every four weeks to the standard maintenance dose of 2.4mg. In January 2026 the MHRA approved a higher maximum dose of 7.2mg weekly for adults with obesity (BMI 30 or above), based on the STEP UP trial. According to the MHRA, this higher dose does not apply to people with a BMI under 30 or to people using Wegovy solely to reduce cardiovascular risk. NICE had not completed an appraisal of the higher dose for NHS use at the time of writing, so check the current SmPC and NICE guidance for the latest position.

Saxenda (liraglutide): the daily option

Liraglutide was the first GLP-1 medicine widely used for weight management. It is shorter-acting, so it needs a daily injection. The dose starts at 0.6mg and rises by 0.6mg each week to 3mg daily.

The Saxenda Summary of Product Characteristics (SmPC) includes a stopping rule: treatment should be stopped if a person has not lost at least 5% of their starting body weight after 12 weeks on the 3mg dose. Our article on Saxenda vs newer GLP-1s looks at where liraglutide fits today.

What the trials show

Every licensed injection was tested in large randomised controlled trials, where people were randomly given the medicine or a placebo (dummy injection), alongside diet and activity advice. This is the most reliable way to measure how much of the weight loss is down to the medicine.

Main placebo-controlled trials

Figures are rounded averages from the published trials and the MHRA announcement for STEP UP. In SURMOUNT-1 the lower doses also produced substantial weight loss: roughly 15% at 5mg and 20% at 10mg.

Averages hide a wide range. In each trial some people lost much more than the average and some lost very little. Weight loss also tends to level off: most of it happens in the first year, after which weight usually plateaus while treatment continues.

The head-to-head trial: SURMOUNT-5

Comparing averages across separate trials is risky, because the people enrolled, the length of follow-up and the methods differ. SURMOUNT-5, published in the New England Journal of Medicine in 2025, compared tirzepatide and semaglutide directly in adults with obesity who did not have diabetes.

Over 72 weeks, people on tirzepatide (at the maximum tolerated dose of 10mg or 15mg) lost about 20% of their body weight on average, compared with about 14% on semaglutide (1.7mg or 2.4mg). Tirzepatide also produced larger average reductions in waist circumference. Gastrointestinal side effects were common with both. The trial was funded by Eli Lilly, the maker of tirzepatide, which is common for trials of this kind and is worth knowing when weighing the results. Our dedicated SURMOUNT-5 guide covers the trial in depth.

There is no published head-to-head trial comparing Mounjaro with the higher 7.2mg Wegovy dose, so how those two compare is not yet known.

Heart health: the SELECT trial

Weight loss is not the only outcome that matters. The SELECT trial (NEJM, 2023) followed more than 17,000 adults with overweight or obesity and established cardiovascular disease, but without diabetes. Semaglutide 2.4mg reduced the risk of major cardiovascular events (heart attack, stroke or cardiovascular death) by about 20% compared with placebo.

On the basis of SELECT, Wegovy's UK licence was extended to include reducing cardiovascular risk in some adults. Tirzepatide is being studied in cardiovascular outcome trials, but at the time of writing Mounjaro does not have a UK licence for that purpose. For more, see our guide to Wegovy and the SELECT trial.

Side effects compared

Because they act on the same pathway, all three injections share a similar pattern of side effects. The most common are gastrointestinal and usually happen when starting treatment or moving up a dose.

"Very common" in an SmPC means more than one in ten people; "common" means up to one in ten. The SmPCs on the electronic medicines compendium (medicines.org.uk) contain the full lists.

A few practical differences are worth noting:

• Injection frequency. A daily injection (Saxenda) means more injections and more needles to dispose of, but some people find a daily routine easier to remember than a weekly one.
• Dose escalation speed. Saxenda steps up weekly, whereas Mounjaro and Wegovy step up no faster than every four weeks. Slower escalation can make side effects easier to manage, and prescribers can hold a dose longer if needed.
• Contraception. The MHRA has advised that tirzepatide may reduce the effectiveness of oral contraceptives, particularly in people who are overweight, and recommends using a non-oral method or adding a barrier method for four weeks after starting Mounjaro and after each dose increase. All GLP-1 medicines should be avoided in pregnancy. See our guide to GLP-1s and contraception.

Serious but rare risks include pancreatitis (inflammation of the pancreas), gallstones and gallbladder inflammation, dehydration from vomiting or diarrhoea leading to kidney problems, and low blood sugar in people also taking insulin or sulfonylureas for diabetes. Our Mounjaro side effects and Wegovy side effects guide cover these in detail.

Practical differences that affect daily life

Pens and injecting

Mounjaro in the UK comes as a KwikPen containing four weekly doses. Each strength is a separate pen, so moving to a new dose means a new pen. Wegovy uses a FlexTouch pen. Saxenda uses a multi-dose pen that is dialled to the daily dose and lasts several days to weeks depending on the dose.

All three need needles attached (or, for some pens, built in), a sharps bin for disposal, and refrigerated storage before first use, with some time allowed at room temperature once in use. Storage details differ by product, so follow the patient information leaflet. Our guide to Mounjaro storage and travel is a useful starting point.

Missed doses

The rules for missed doses differ:

• Mounjaro: if it is four days (96 hours) or less since the missed dose, take it as soon as possible; otherwise skip it and take the next dose on the usual day.
• Wegovy: if it is five days or less since the missed dose, take it as soon as possible; otherwise skip it.
• Saxenda: if it is within 12 hours of the usual time, take it; otherwise skip that day's dose. Missing three or more days may mean restarting at a lower dose.

These are summaries; always check the patient information leaflet and speak to your prescriber if you miss several doses, because restarting at your previous dose can cause stronger side effects. See Mounjaro missed dose.

Stopping treatment

Weight regain after stopping is common with all GLP-1 medicines. In the STEP 1 extension, people who stopped semaglutide regained around two-thirds of the weight they had lost within a year. In SURMOUNT-4, people who were switched from tirzepatide to placebo after 36 weeks regained a meaningful proportion of their lost weight, while those who continued kept losing. This does not mean treatment is pointless if stopped, but it does mean planning for the long term matters. Our guides to Mounjaro maintenance and weight regain after stopping explore this.

NHS access compared

NICE decides whether a medicine is cost-effective enough for routine NHS use in England, and its decisions are generally followed in Wales and Northern Ireland. Scotland has its own body, the Scottish Medicines Consortium.

The NHS roll-out of Mounjaro is phased. NHS England's interim commissioning guidance prioritised, in the first year from June 2025, people with a BMI of 40 or more (adjusted for ethnicity) and at least four of five named conditions: type 2 diabetes, high blood pressure, heart disease, obstructive sleep apnoea and abnormal blood fats. Later cohorts widen the criteria. Local availability varies between integrated care boards. See our guides to Mounjaro on the NHS and private vs NHS weight loss treatment.

Cost: what affects it

We do not quote prices in our guides, because they change often and differ between providers. Several things affect what you might pay privately:

• The medicine and dose. Prices often vary by strength, and some providers charge more for higher doses.
• List price changes. In September 2025 Eli Lilly raised the UK list price of Mounjaro for private supply. The NHS price was not affected. Our article on the 2025 Mounjaro price rise explains what happened.
• What is included. Some providers include consultations, needles, sharps bins and clinical follow-up; others charge separately.
• Frequency. A daily injection may need more pens or needles over time than a weekly one.

For a fuller explanation, read how weight loss injection pricing works, and use our price comparison to see how regulated providers compare on service.

Oral alternatives

Injections are no longer the only option. At the time of writing, the MHRA has authorised two GLP-1 tablets for weight management: the Wegovy tablet (oral semaglutide), approved in 2026, and Foundayo (orforglipron), approved in August 2026. Neither had completed NICE appraisal for NHS use at the time of writing. Their availability and licensed details may change, so check the MHRA and the current SmPC. Our guide to oral vs injectable GLP-1s compares the two routes.

How a prescriber might choose between them

There is no universal ranking. A prescriber will usually weigh:

1. Your health goals and conditions. For someone with established heart disease, the cardiovascular evidence for Wegovy may be relevant. For someone prioritising the greatest likely weight loss, trial data favour tirzepatide on average.
2. Previous experience. If you have tried one GLP-1 medicine and had intolerable side effects or little response, a different option may be considered.
3. Other medicines. Particularly diabetes medicines that can cause low blood sugar, oral contraceptives, and medicines where slowed stomach emptying matters.
4. Medical history. Pancreatitis, gallbladder disease, severe gastrointestinal disease, diabetic eye disease, kidney problems, thyroid cancer history and eating disorders all need careful assessment.
5. Practicalities. Daily vs weekly injecting, dexterity, storage, supply and how you access care (NHS or private).
6. Cost and access. NHS eligibility is limited, and private costs differ between medicines and providers.

The aim is the medicine you can take safely and consistently, with appropriate monitoring and support, rather than the one with the biggest headline number. You can compare regulated services on our providers page.

When to speak to a professional

Speak to your GP, a pharmacist or your prescriber before starting, switching or stopping any weight loss injection. They can check whether treatment is suitable, review your other medicines and arrange monitoring. Tell them if you are pregnant, planning a pregnancy or breastfeeding, have had pancreatitis or gallbladder problems, have diabetes or diabetic eye disease, or have a history of an eating disorder.

Seek urgent medical help (call NHS 111, or 999 in an emergency) if you experience:

• severe, persistent abdominal pain, which may spread to your back, with or without vomiting (possible pancreatitis)
• pain in the upper right of your abdomen, fever, or yellowing of the skin or eyes (possible gallbladder problems)
• persistent vomiting or diarrhoea leading to signs of dehydration, such as dizziness, very dark urine or passing very little urine
• signs of a severe allergic reaction, such as swelling of the face, lips or throat, or difficulty breathing
• symptoms of low blood sugar if you also take diabetes medicines, such as shaking, sweating, confusion or drowsiness
• new or worsening low mood, or thoughts of self-harm

You can report suspected side effects through the MHRA Yellow Card scheme.