The different types of weight loss injections available in the UK

You've searched 'weight loss injections' and found three or four names, here's what they actually are

It's a reasonable source of confusion. Mounjaro, Wegovy, Ozempic, Saxenda, all come up in the same search, none of them are exactly household names yet, and the articles about them often use the brand names and the drug names interchangeably. So let's be direct.

The two injections licensed in the UK specifically for weight management are tirzepatide (brand name Mounjaro, made by Eli Lilly) and semaglutide (brand name Wegovy, made by Novo Nordisk). Both are given as a once-weekly injection under the skin, typically into the abdomen, thigh or upper arm. You can read more about both on the weight loss injections overview page.

Ozempic is also semaglutide, but it is licensed for type 2 diabetes management, not weight loss. Saxenda (liraglutide) is UK-licensed for weight management but is a daily injection rather than weekly, and the clinical evidence behind the newer weekly medicines is considerably stronger. The NHS medicines page on tirzepatide sets out its approved uses clearly if you want the official summary.

Wegovy tablets (oral semaglutide) received MHRA approval in June 2026 as a separate licensed option, but that's a different format from the injection. The focus here is the injections specifically.

The key difference between the two injections: one pathway or two

Both Mounjaro and Wegovy belong to a class of medicines called GLP-1 receptor agonists. They mimic a gut hormone released after eating, slowing how quickly the stomach empties and sending satiety signals to the brain. That's where the similarity ends mechanically.

Wegovy (semaglutide) acts on the GLP-1 receptor only. Mounjaro (tirzepatide) acts on both the GLP-1 and GIP receptors, making it the only dual-agonist weight-loss injection licensed in the UK. GIP is a second gut hormone involved in energy balance, and activating both pathways appears to produce a stronger effect on average weight loss in trials.

The SURMOUNT-1 trial, involving over 2,500 adults with obesity and no diabetes, found average body-weight reductions of around 20–21% at the highest dose over 72 weeks. The STEP 1 trial, published in the New England Journal of Medicine, reported around 15% average weight loss with semaglutide 2.4mg at 68 weeks. In the 2025 SURMOUNT-5 head-to-head trial, tirzepatide produced greater average weight loss than semaglutide 2.4mg over 72 weeks.

Those are population averages from clinical trials, not individual predictions. A prescriber considers your full picture before recommending which injection is appropriate for you, and whether either is suitable at all. If you're weighing up the options in more detail, the guide to the differences between weight loss injections goes further on this comparison.

What the titration schedule looks like in practice

Neither injection starts at its maximum dose. Both begin low and increase gradually (a process called titration) to give your body time to adjust and reduce the likelihood of side effects, which are mostly gastrointestinal.

Mounjaro is supplied as a KwikPen. Treatment starts at 2.5mg weekly, typically increasing every four weeks through 5mg, 7.5mg, 10mg, 12.5mg up to a maximum of 15mg. The pace and ceiling are decided by your prescriber based on how you're tolerating the medicine. Wegovy follows a similar pattern, starting at 0.25mg and escalating through 0.5mg, 1.0mg, 1.7mg to a standard maintenance dose of 2.4mg; the MHRA approved a higher 7.2mg dose in January 2026, with a single-dose pen for that strength approved in April 2026.

Both medicines are injected once weekly on the same day each week and stored in the fridge at 2–8°C. Your Patient Information Leaflet sets out the permitted room-temperature window, defer to that rather than any general statement online. The pen itself is discreet and pre-filled; if ordered through a regulated online pharmacy, it arrives in plain, unbranded packaging with DPD tracking so you know exactly when it's coming. Safe disposal matters: a 1-litre sharps container is the appropriate way to dispose of used pens in the UK.

For a fuller picture of how accessing one of these injections works, the weight loss injection guide covers the process from consultation to delivery.

Side effects, who these injections suit, and the cost question

The side-effect profile for both injections is broadly similar: nausea, loose stools, constipation, indigestion, burping and fatigue are the most commonly reported, usually most noticeable after starting or after a dose increase. Most people find these settle within a week or two. Symptoms are rarely a reason to stop, but they're also not nothing, and your prescriber needs to know if they're severe or persistent.

Pancreatitis is a rarer but more serious risk. The MHRA issued a Drug Safety Update in January 2026 highlighting this: severe, persistent stomach pain that radiates to the back (with or without vomiting) warrants urgent medical attention. Any suspected side effects can be reported at yellowcard.mhra.gov.uk.

Neither injection is licensed for under-18s. Neither is recommended during pregnancy, breastfeeding, or when trying to conceive. Women using oral contraceptives alongside tirzepatide should add a non-oral method for the first four weeks of treatment and for four weeks after each dose increase, as GI slowing can reduce pill absorption, there is no equivalent advisory for semaglutide. If you want to understand the different kinds of weight loss injections available, including how they differ by mechanism and licensing, that page sets out the landscape clearly before you reach the consultation stage. These details matter, and they're exactly the sort of thing a prescriber discusses at consultation.

On cost: private treatment for either injection is priced per pen per month and varies by dose and provider. If cost is a factor, the guide to the cost of weight loss injections in the UK explains what typical market prices reflect and what they often leave out. The short version is that the prescription, clinical oversight and aftercare built into a regulated service are the parts worth paying for, the medicine is the same wherever the pen comes from, but the clinical care around it isn't. There is no legitimate discount code for a prescription-only medicine.

If you'd like to understand whether you'd be eligible for either injection, check your eligibility with our clinical team. A GPhC-registered prescriber reads every consultation personally, the same day it arrives.