Liraglutide vs Mounjaro: what the evidence actually shows

The trial data: where the numbers diverge

Liraglutide's pivotal SCALE trial (published in the New England Journal of Medicine) reported an average weight reduction of around 8% over 56 weeks in adults with obesity, alongside lifestyle changes. That was a meaningful step forward when it was published. Then tirzepatide arrived.

SURMOUNT-1, the pivotal trial for Mounjaro, ran for 72 weeks with 2,539 adults with obesity. At the 15 mg dose, participants lost an average of around 20–21% of body weight, roughly two and a half times the liraglutide figure. NICE's appraisal of tirzepatide (TA1026) drew on this data directly, recommending the medicine for NHS use on the basis of both its clinical outcomes and its cost-effectiveness modelling.

Neither of these figures is a promise for any individual. Trial populations are controlled; real-world results vary. What the data does tell you is that, on average and at comparable points in treatment, tirzepatide produced substantially greater reductions, and if you want to see those results set side by side in detail, the tirzepatide vs liraglutide comparison page walks through the numbers from both trials. A fuller breakdown of the tirzepatide trial results is on the Mounjaro overview page.

Mechanism: why one pathway versus two changes things

Liraglutide mimics glucagon-like peptide-1 (GLP-1), a gut hormone that signals fullness to the brain, slows the rate at which the stomach empties, and nudges the pancreas to release insulin in response to food. It does one job well.

Tirzepatide adds a second receptor into that picture. It activates GIP (glucose-dependent insulinotropic polypeptide) alongside GLP-1. GIP receptors are present in fat tissue and the brain as well as the gut, and the dual action appears to compound the appetite-suppression effect beyond what single-pathway agents achieve. The NHS medicines page for tirzepatide explains the mechanism in plain terms.

This dual agonism is the structural reason the trial numbers look so different. It is also why researchers exploring what comes next (you can read about one candidate on the retatrutide vs Mounjaro page) are building on multi-receptor approaches rather than returning to single-pathway designs.

If you are curious how tirzepatide compares more broadly across the GLP-1 class, the dulaglutide vs tirzepatide page covers another single-agonist comparison.

Licences, availability, and what nume does and does not dispense

Both medicines are licensed for weight management in the UK. Liraglutide (Saxenda) holds a UK marketing authorisation for adults with BMI 30 or above, or 27 and above with a weight-related condition. Mounjaro holds equivalent licensing, also at those thresholds, and carries a Black Triangle (▼) designation indicating additional MHRA monitoring as a newer medicine.

It is worth being direct here: nume does not dispense liraglutide for weight loss. If liraglutide is something you are currently taking or have been recommended, the right conversation is with your GP or current prescriber. What the weight-loss treatments page covers is Mounjaro and Wegovy, both of which are available through nume's private prescription service following a clinical assessment.

If you are already on liraglutide and wondering whether switching makes sense, that is a specific clinical question, and one the switching from liraglutide to tirzepatide page addresses in more detail.

Patients sometimes ask their GP about Mounjaro; the page on asking your GP for Mounjaro is a useful read before that conversation.

Side-effect profiles and a note on tolerability

The two medicines share a broadly similar tolerability pattern because both slow gastric emptying. Nausea, loose stools, constipation, indigestion, and fatigue are the most commonly reported side effects with each. These tend to be most noticeable after starting treatment or moving to a higher dose, and they often settle within a couple of weeks.

Where they differ slightly is in the frequency and intensity reported in trials. Liraglutide is a daily injection; tirzepatide is once weekly. Some people find daily dosing a meaningful burden; others prefer a more familiar routine. That is not a clinical argument, it is a practical one, and it matters.

The NHS tirzepatide medicines page carries the full side-effect list for Mounjaro. The patient information leaflet supplied with any dispensed medicine is always the definitive reference for your specific dose and health history.

If you find yourself weighing up these two medicines and feeling genuinely uncertain, that is completely reasonable. The literature is dense, the branded names multiply, and the numbers get quoted out of context constantly. The clearest path through is usually a conversation with a prescriber who can look at your actual situation, which is exactly what the free consultation at nume is designed for.