Wegovy 0.25mg vs Mounjaro 2.5mg: comparing the starter doses

Step 1 — Understand what a starter dose is actually doing

There is a common misconception that the first pen or first few weeks of treatment are the phase where weight loss happens. They are not. Both Wegovy 0.25mg and Mounjaro 2.5mg exist for one reason: to reduce the chance of nausea, vomiting and other gastrointestinal side effects as your body meets a new medicine for the first time. Weight loss at these doses, if it occurs at all, is incidental.

Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, the only weight-loss medicine licensed in the UK that activates both pathways simultaneously. Wegovy (semaglutide) is a GLP-1 receptor agonist, acting on a single pathway. Both slow gastric emptying and reduce appetite, but the underlying pharmacology is meaningfully different. The NHS patient information page on tirzepatide and the equivalent page for semaglutide explain this well if you want the full picture before your consultation. Because the mechanisms differ, the dose numbers carry different weights, and if you are wondering whether 0.25mg Wegovy is the same as 2.5mg Mounjaro, the short answer is that you cannot directly convert one into the other. Our page on what 0.25mg Wegovy is equivalent to in Mounjaro terms explores that question properly.

Both medicines are licensed for adults with a BMI of 30 or above, or 27 or above alongside at least one weight-related health condition. Lower thresholds apply for some ethnic backgrounds under UK guidance. A prescriber assesses the full picture before any dose is issued.

Step 2, Compare the titration paths from each starting point

From 0.25mg, Wegovy typically moves through 0.5mg, 1.0mg, 1.7mg and then to the standard maintenance dose of 2.4mg, with each step taken roughly four weeks apart. A higher 7.2mg dose is now also MHRA-approved for eligible patients. From 2.5mg, Mounjaro follows a similar four-week step pattern up through 5mg, 7.5mg, 10mg, 12.5mg and 15mg. The ceiling is different, the step count is different, and the prescriber decides the pace based on how each patient tolerates each level.

Titration is not a race. A prescriber may hold a patient at a lower dose for longer if their tolerance calls for it. This is one reason the broader Wegovy vs Mounjaro comparison cannot be reduced to a single number, the dose at which someone settles long-term depends on individual response and clinical judgement, not the label on the starter pen.

In the SURMOUNT-5 head-to-head trial, published in the New England Journal of Medicine in 2025, tirzepatide produced a greater average weight reduction than semaglutide 2.4mg over 72 weeks in adults with obesity and without diabetes. NICE's appraisal of tirzepatide (TA1026) references this indirect advantage. That evidence applies to the full therapeutic doses, though, not the starter doses discussed here.

Step 3, Read the side-effect profiles at starting doses

The side effects at 0.25mg Wegovy and 2.5mg Mounjaro tend to be milder than those seen at higher doses, precisely because these are the lowest rungs of their respective schedules. Nausea is the most commonly reported symptom on both, followed by loose stools, constipation, indigestion and fatigue. Most people find these settle within the first week or two of a new dose level.

One thing worth flagging, particularly for women: if you are using the oral contraceptive pill while starting Mounjaro, MHRA and NHS guidance advises adding a non-oral method of contraception for the first four weeks of treatment and for four weeks after each dose increase, because tirzepatide may reduce pill absorption. NHS England's guidance on weight-management injections covers this in detail. The equivalent evidence does not apply to Wegovy.

If you experience severe or persistent stomach pain that spreads to your back, with or without vomiting, seek medical help promptly, this is the presentation associated with acute pancreatitis, which the MHRA has highlighted as a known but infrequent risk with GLP-1 medicines. Report any suspected side effects through the Yellow Card scheme.

Side-by-side: starter dose facts at a glance

Numbers cited from the eMC SmPCs for Mounjaro and Wegovy respectively. The full dose schedules, storage conditions and contraindication lists are set out there; a prescriber applies them to your specific situation.

Which of these suits you is not a question the starter dose answers. It is a clinical decision our prescribers work through with you. You can explore the cost context separately on our Wegovy vs Mounjaro cost page, and if you are curious about how 0.25mg Wegovy compares to Mounjaro across the two medicines more broadly, that page sets out the key differences in one place. If you want to understand how the available strengths of each medicine stack up against one another, our guide to Wegovy mg vs Mounjaro walks through the full dose ranges side by side. When you are ready, start your free consultation and a prescriber will review your answers the same day.