How your Mounjaro weekly dose works — and what shapes the decision

The 2.5 mg starting point is about tolerance, not results

The first weekly dose of Mounjaro is 2.5 mg, and it is worth being clear about what that pen is for. Its job is not to produce rapid weight loss. It is to give your digestive system time to adapt to the way tirzepatide slows gastric emptying and signals fullness through two gut-hormone pathways, GIP and GLP-1. Starting lower reduces the intensity of nausea and other gastrointestinal effects that tend to be sharpest in the early weeks. The clinical evidence behind this schedule is well-established: the phase 3 trials in the SURMOUNT programme that informed NICE's appraisal of tirzepatide all used this stepped approach, and the mean weight reductions of around 20–21% at 15 mg emerged from a protocol that began at 2.5 mg and moved up deliberately.

Practically, this means most people notice very little weight change in the first four weeks. That is normal and intended. Expecting more from the starter dose is the single biggest source of early anxiety in our consultations. Give it the month it needs.

For a full picture of how the six strengths map against one another, the tirzepatide dosage chart lays out the schedule clearly.

How a prescriber decides whether to move your dose up

No algorithm bumps your Mounjaro dose automatically. At nume, sorry, at nume, before any repeat order is dispensed, a GPhC-registered Independent Prescriber reads your update. They are looking at several things: how you have tolerated the current dose, whether side effects have settled, any relevant changes to your health or other medicines, and whether your weight trajectory is consistent with continued treatment.

Dose increases generally happen in 2.5 mg steps after a minimum of four weeks at the current level, so from 2.5 mg to 5 mg, then 7.5 mg, and so on. The prescriber may decide to stay at a dose longer if tolerability is still a work in progress. There is no clinical benefit in rushing upward if nausea is still prominent. Equally, if a lower dose is managing both tolerability and progress well, remaining there is a legitimate outcome. The ceiling is 15 mg; not everyone reaches it, and not everyone needs to.

If you want to understand more about what the 5 mg step involves specifically, the Mounjaro 5 mg page covers the evidence and practical points for that dose in detail.

Timing rules: why the weekly interval matters

Once-weekly means every seven days. That consistency matters because tirzepatide's pharmacokinetics (the way the drug builds up and clears) are built around a weekly rhythm. The day itself can be changed if you have a good reason, but the interval between doses should stay close to seven days; stretching or shortening it significantly can affect both tolerability and efficacy.

What happens if you miss a dose is a question that comes up regularly. The short answer is that it depends on how long ago it was due. The guidance on a missed dose page covers the one-week scenario, and if a gap of two weeks has opened up, the two-week missed dose page addresses that separately. Both defer to your Patient Information Leaflet and prescriber, as they should. And if you have ever wondered about the logic of taking two doses closer together, the answer to that question is not what most people hope.

Store your pen in the fridge at 2–8°C. There is a limited window for room-temperature storage if needed while travelling, the exact duration is stated in the SmPC, and the NHS tirzepatide medicines page summarises it for patients. Always check the leaflet rather than relying on a general figure.

When NICE guidance suggests stepping back and reviewing

NICE recommends that if someone on tirzepatide has lost less than 5% of their body weight after six months at the highest tolerated dose, continuing treatment should be reconsidered. This is a clinical checkpoint, not an automatic stop, but it exists for a reason: the medicine does not produce the same response in everyone, and ongoing use without meaningful benefit is not in a patient's interest.

This threshold is one reason why evidence-based clinical review before each repeat matters, not as a bureaucratic hurdle but as a genuine safety check. For context on Mounjaro's licensed indications and UK evidence base more broadly, including the SURMOUNT trial results, that page covers the full picture. Cost context sits on the buy Mounjaro online page, including how private treatment is priced in the UK and what a legitimate prescription includes.

If you are considering starting treatment or have questions about whether your current dose is right, the clearest next step is a clinical conversation. Check your eligibility with our prescribers, the consultation is free, and a real clinician reviews your answers the same day.