Trulicity vs Mounjaro: Understanding the Difference

Why the licence question matters more than the mechanism

Both dulaglutide (Trulicity) and tirzepatide (Mounjaro) act on receptors involved in insulin release and appetite signalling. Trulicity works on one receptor, GLP-1. Mounjaro activates two (GLP-1 and GIP) making it the only dual-agonist weight-loss medicine currently licensed in the UK.

That mechanistic difference is interesting, but the more important distinction is regulatory. Trulicity holds a UK licence for type 2 diabetes management. It does not hold a licence for weight management. Mounjaro, by contrast, holds both: it is licensed for type 2 diabetes and, separately, for weight management in adults with a BMI of 30 or above, or 27 or above where a weight-related condition such as high blood pressure or obstructive sleep apnoea is present. The NICE appraisal of tirzepatide (TA1026) confirmed its recommendation for NHS use in eligible adults.

For anyone whose primary concern is body weight, this means only one of these two medicines has an established, appraised evidence base for that goal, and only one can be legally prescribed for it. A prescriber can, in some circumstances, prescribe outside a medicine's licensed indication, but that is a clinical decision made for specific individual reasons, not a shortcut around the approval process.

Worth doing in under a minute: check any online pharmacy you are considering against the GPhC register at pharmacyregulation.org/registers. If it is not listed, do not order from it.

How the weight-loss evidence compares

Trulicity's clinical programme was designed around glycaemic control in type 2 diabetes, not weight. Some weight reduction was observed as a secondary effect in those trials, but the doses studied and the outcomes measured were not set up to answer a weight-management question, and Lilly has not sought a weight-management licence for it in the UK.

Mounjaro's SURMOUNT programme did set out to answer that question. In SURMOUNT-1, which enrolled 2,539 adults with obesity and without diabetes, average body-weight reduction at the 15mg dose over 72 weeks was around 20 to 21%, as published in the New England Journal of Medicine. A later head-to-head trial, SURMOUNT-5, compared tirzepatide directly with semaglutide 2.4mg and found greater average weight reduction with tirzepatide, the first controlled comparison of its kind at the relevant doses.

These figures come from clinical trials under controlled conditions. Individual results vary. What the data does tell you is that tirzepatide's weight-related evidence base is large, rigorously studied and appraised by NICE specifically for the purpose readers of this page are interested in. Trulicity's is not. You can explore how Mounjaro's results compare to other GLP-1 approaches on our dedicated page covering GLP-1 versus Mounjaro.

Side effects and practical differences between the two

Because Trulicity is not licensed for weight management in the UK, a detailed side-effect comparison framed around weight-loss treatment would be misleading. What can be said is that both medicines share a broadly similar tolerability profile given the GLP-1 pathway they both activate: nausea, loose stools, reduced appetite and, less commonly, vomiting or reflux. With Mounjaro, the additional GIP activity adds complexity that a prescriber will walk through with you.

The NHS's medicines information on tirzepatide covers common and serious side effects in plain language, and is the right starting point for anyone researching what to expect. Both medicines come as pre-filled pens injected once a week into the abdomen, thigh or upper arm.

One practical note: women using oral contraceptives alongside tirzepatide are advised to add a non-oral method for the first four weeks of treatment and for four weeks after each dose increase, because Mounjaro can reduce how much of the pill is absorbed. This does not apply to Trulicity in the same documented way. If HRT is part of your routine, discuss the formulation with your prescriber before starting either medicine.

Which one can you actually get for weight management, and through whom?

Trulicity is not something a prescriber can legitimately issue for weight loss in ordinary private practice, because the licence does not support it. If you see it offered that way by an online seller, that is a serious red flag. The MHRA has consistently warned that medicines sold for purposes outside their licence (particularly injectable weight-loss products) are a source of counterfeit and unsafe supply. Report any suspicious sellers at yellowcard.mhra.gov.uk.

Mounjaro, prescribed for weight management, is available privately through a GPhC-registered pharmacy following clinical assessment. At nume, a GPhC-registered Independent Prescriber personally reviews every consultation. There is no algorithm making the call. For anyone who meets eligibility criteria, Mounjaro is also entering NHS availability on a phased rollout, though criteria are strict and waiting times vary. The eligibility guide on this site sets out both the private and NHS thresholds in plain terms.

If you are weighing Mounjaro against other newer compounds rather than older diabetes medicines, our page comparing retatrutide and Mounjaro covers how a triple-agonist candidate stacks up against the currently licensed option, and our overview of how Mounjaro works will cover the detail. If you want to understand exactly how tirzepatide relates to the drug class it belongs to, our page explaining tirzepatide versus Mounjaro unpacks that clearly. For a broader look at weight-loss treatment options, start with a free consultation and let a prescriber map the right path with you. Which medicine suits your circumstances is precisely the kind of decision that belongs in a clinical conversation, not a search result.