Missed a Mounjaro injection — what should you do?

What does the four-day rule actually mean in practice?

Mounjaro is taken once weekly, and the prescribing information sets out what to do when a dose is missed. The key dividing line is whether there are at least four full days between now and your next scheduled injection. If there are, take the missed dose as soon as you remember and then keep your original day of the week going forward. If the gap is shorter than four days, leave the missed dose where it is and carry on as normal next week.

A practical example: say you normally inject on a Monday but you reach Wednesday and realise you forgot. Your next dose would be the following Monday (five days away) so Wednesday works fine. But if it is already Friday or later, that leaves fewer than four days to Monday, so you would skip it and simply inject on Monday as planned.

This guidance comes from the Mounjaro patient information leaflet and is consistent with the NHS's tirzepatide medicine page. If you are ever unsure about the count, the leaflet that came with your pen is the right first place to check. You can also contact our team if you want to talk it through.

Will missing a dose affect how the medicine is working?

One skipped injection is not going to undo the progress you have made. Tirzepatide has a half-life of around five days, which means meaningful amounts of the medicine remain active in your system well beyond your usual injection window. You may notice that appetite returns a little or that you feel slightly less full than usual in the days after a missed dose, that is normal physiology, not a sign that treatment has stopped working.

A common worry at this point is that the missed dose counts as a "reset" and requires starting the titration schedule again from 2.5mg. It does not. You pick up at whichever strength you were already taking and continue from there. The titration schedule exists to help your body adjust gradually to the medicine, once that adjustment has happened, a brief interruption does not reverse it.

Where longer gaps do matter is if treatment is paused for several weeks or more. In those cases, your prescriber may want to reconsider your dose before you restart. That is a conversation worth having before resuming rather than after. Our guide to Mounjaro's dose schedule explains the full titration pathway for context.

Are there any side effects to expect when you resume?

Some people find that gastrointestinal symptoms (nausea, loose stools, or a feeling of fullness) are a little more noticeable in the day or two after resuming, particularly if several days have passed. This mirrors what many experience when moving up a dose: the body readjusts briefly. It tends to settle quickly.

Eating smaller, lower-fat meals and staying well hydrated on the day you resume can help. The NHS medicines information for tirzepatide lists the most common side effects and describes the pattern, generally most pronounced in the early weeks of treatment or after a dose increase, then easing.

One side effect worth knowing about is pancreatitis, which is rare but serious. The MHRA has highlighted severe, persistent stomach pain that may spread to the back as a symptom requiring prompt medical attention. This applies throughout treatment, not specifically after a missed dose, but it is worth knowing. Report any suspected side effects through the Yellow Card scheme. If you have a question that feels more pressing, you can always reach the answers to our most common questions or speak to our clinical team directly.

For anyone currently weighing up whether Mounjaro is the right option for them, information on the wider treatment and how it works may be useful context, including on starting a consultation with our prescribers.

When should you speak to a prescriber rather than handling it yourself?

Most missed-dose situations are genuinely self-manageable using the four-day rule above. There are a few circumstances where speaking to a prescriber first is the better call. If you have missed multiple doses in a row (say, more than two weeks have passed) it is sensible to check in before restarting, since your prescriber may want to review your dose. Similarly, if you missed a dose because of a significant illness involving vomiting or diarrhoea, they may want to consider whether dehydration or another factor needs addressing first.

If you are considering a dose change alongside resuming, for example if you have been on tirzepatide 5mg/0.6ml for several months and wanted to move up, that decision needs a clinical review anyway, not just a timing adjustment. Dose increases at nume are assessed individually before dispatch; our prescribers look at your progress and any side effects you have experienced at the current level before approving a move upward.

And if your situation is more complex (you are on other medicines, you have recently had surgery, or you have a health condition that affects how you absorb or tolerate Mounjaro) a quick word with your prescriber is always time well spent. You can find information about the clinical team behind nume's reviews on the clinical team page. Separately, if you are thinking about the cost of staying on treatment long-term, the treatment overview covers what is included in the price at each step, including details on options such as the Mounjaro injection 5mg pen, Mounjaro injection 10mg and the Mounjaro injection 10 mg pen format.