Missing a Week of Mounjaro: What Actually Happens

What the licensed prescribing instructions actually say

The Mounjaro Summary of Product Characteristics, published on the electronic Medicines Compendium, sets out the missed-dose rule in precise terms: administer the injection as soon as you remember, then resume on your original weekly schedule. The caveat is the four-day window. If your next planned injection is four or more days away, you can still take the missed dose. If it's fewer than four days away, leave it and continue from your regular day as normal.

One thing the SmPC is unambiguous about: do not inject two doses to make up for the one you missed. Tirzepatide is a dual GIP and GLP-1 receptor agonist (the only medicine of its kind licensed in the UK for weight management) and its gastrointestinal side-effect profile means an accidental double-dose could produce a sharp spike in nausea or vomiting without any clinical benefit. The tirzepatide information page explains the mechanism in more detail if you want the pharmacology.

It's also worth knowing that the four-day rule applies to all strengths, from the 2.5 mg starting pen right through to the 15 mg maintenance dose. The strength does not change what you should do.

Why one missed week rarely derails your progress

Tirzepatide's pharmacokinetics help explain why missing a single injection is less disruptive than it might feel. The medicine has an approximate half-life of roughly five days, which means it clears from the body gradually. After seven days without a dose, a meaningful amount is still circulating; after fourteen days, the picture changes more noticeably. This pharmacological cushion is part of why the SURMOUNT clinical trial programme (which enrolled thousands of adults with obesity) observed that participants who experienced brief interruptions in dosing did not see their weight simply rebound overnight.

That said, you may notice the gap. Appetite often edges back before your next dose, and some people find their energy or sense of fullness feels slightly different in the days before a delayed injection. This is normal physiology, not a sign that the treatment has stopped working. If you're concerned about how a missed week sits alongside your titration plan, the question of whether it's safe to miss a week of Mounjaro has more detail on the clinical thinking behind this.

The SURMOUNT-1 trial, published in the New England Journal of Medicine, reported average body-weight reductions of around 20–21% at 72 weeks at the 15 mg dose, results achieved across a population that included real-world adherence variation, not a perfect-compliance cohort. One week is unlikely to be the deciding factor in your outcome.

When a missed week becomes a longer gap

A single missed injection and a two-week gap are different situations. If more than two weeks have passed since your last Mounjaro dose, the SmPC guidance is to restart at 2.5 mg (the same tolerability starting dose used at the beginning of treatment) and work back up through the titration steps. This is not a punishment; it reflects the fact that your gastrointestinal tolerance to the medicine will have reduced during the break, and restarting at a higher dose increases the risk of side effects without improving outcomes.

If you've missed two weeks and are unsure what to do next, the guide to missing two weeks of Mounjaro covers the retitration process in full. And if you're wondering whether it's ever appropriate to delay a dose intentionally, for surgery or travel, that's worth discussing with your prescriber directly rather than making the call yourself.

A useful reference point from the NHS tirzepatide patient information page: the NHS echoes the SmPC's missed-dose instructions and adds that if you are unsure what to do, you should contact your pharmacist or doctor. That advice stands regardless of where you source your prescription.

Keeping your routine solid to reduce missed doses

Most missed doses happen not from carelessness but from disrupted routines: a holiday where the pen stayed in the hotel fridge, a busy week where Thursday slipped by unnoticed. The simplest protection is a consistent injection day tied to something fixed in your week, and storing your pen where you'll actually see it, next to something you open daily, whether that's the fridge shelf at eye level or a drawer by the bathroom sink.

If supply disruptions are behind a missed week rather than a forgotten dose, that's a separate conversation. Checking the background on Mounjaro supply and pricing in the UK gives context on what's happened in the market, including the 2025 Eli Lilly list-price changes that affected many providers. Consistency of supply is one reason our prescribers at nume treat it as a clinical concern, not just a logistics one.

If you're approaching week five of treatment and wondering whether your progress is on track, the week five milestone page offers a realistic picture of what most people notice at that point. And if you have questions about your own situation that this page hasn't answered, what to do if you miss a week of Mounjaro walks through the decision step by step.

Mounjaro is a prescription-only medicine, and every repeat supply at nume is reviewed by a GPhC-registered independent prescriber before dispatch. If you've had a difficult few weeks and want clinical support around your schedule, check your eligibility and speak to the prescribing team.