Forgot Your Mounjaro Dose? What to Do (October 2026)

01 · Core answer

What to do right now if you forgot your Mounjaro dose

Work out how long ago your injection was due.

If you miss a dose, take it as soon as you can within 4 days (96 hours) of the scheduled time, then carry on with your usual day.¹ If more than 4 days have passed, skip the missed dose entirely and take the next one on your normal day — never take two doses within 3 days of each other.¹

You do not need to compensate for the lost dose, and you should not inject extra medicine to make up for it. Our related guide on a missed injection walks through the same steps from the pen side.

02 · Decision

How the rule works in practice

The easiest way to apply the rule is to count from your usual injection day. These examples use a Monday injection day and avoid the edge of the window, so you can see the logic clearly.

If you are unsure whether you are inside the window, check the date on your last injection in your notes or in a tracking app. Our free GLPTrackr companion app is designed for exactly this kind of record keeping. When in doubt, ask the pharmacy or your prescriber before injecting rather than guessing.

03 · Next step

Should you change your injection day?

Only if the new day suits you better, and only with a safe gap. You can change your weekly injection day if needed, as long as at least 3 days (72 hours) have passed since your last dose.¹

If your original day clashes with work or travel, you may want to move it. If you are running low and need to plan ahead, see the Mounjaro pen prices and consultation page, where a GPhC-registered prescriber reviews every order.

04 · Why timing matters

Why the missed-dose window exists

The window exists because Mounjaro is built around a steady weekly rhythm.

Tirzepatide has a half-life of about five days, which is why a weekly schedule works at all. After a final dose it takes roughly four to five weeks to clear the system.¹

The rule against doubling up follows the same logic. Never take two doses within 3 days of each other.¹

If you are early in treatment, our guide to Mounjaro stages shows where each dose fits in the overall journey, which can help you judge how much a slip matters at your point.

05 · Effects of a missed dose

What to expect after a missed or late dose

Mounjaro works by activating the GIP and GLP-1 receptors, which help regulate appetite and slow how quickly the stomach empties.¹

Weight loss on Mounjaro is gradual by design. Trials measured results at 72 weeks, so think in months, not days, and judge progress by trend rather than individual weigh-ins.² One skipped week is a small point on a long curve.

Early loss also includes water weight, so the scale can move around in the first weeks regardless of whether you missed an injection.

Because tolerability varies, it is worth telling your prescriber if a missed dose is followed by side effects that worry you, or if you start to feel unwell. You can also report any suspected side effect through the Yellow Card scheme.¹⁹

06 · Early doses and restarting

Missing a dose on the starting dose or after a dose increase

The same rule applies at every strength, but the stakes feel different at the start. Everyone begins on 2.5mg once a week, and that starting dose is about letting your body adjust rather than weight loss itself.¹ If you slip on this dose, follow the missed-dose rule and carry on.

Dose increases happen at a minimum of four-week intervals, depending on how you respond and tolerate treatment. Your prescriber sets the pace, so mention a missed injection at your next review. Our pages on the Mounjaro smallest dose and the Mounjaro beginner dose explain what the first weeks involve.

If you have missed several injections in a row, do not simply inject at the strength you were last on. Ask your prescriber how to resume. Do not decide this yourself.

Never try to make up for lost time by taking extra medicine from a pen.

07 · Pen and storage checks

Pen and storage checks before a late injection

A late dose is a good moment to check the pen itself.

Check how long the pen has been in use too. Keep Mounjaro pens in a fridge at 2–8°C and never freeze them. Once in use, a pen can be kept out of the fridge not above 30°C for up to 30 days, after which it should be discarded.¹ Keep the cap on to protect it from light.

If you cannot tell whether a pen is still suitable, for example because it was left out of the fridge, our guide to forgetting to refrigerate Mounjaro explains what to check. For an unopened pen that has been out of the fridge, check with the pharmacy before using it rather than relying on a remembered day limit.¹

08 · Never forgetting again

How to stop forgetting your weekly dose

The most reliable fix is a fixed day and a reminder. There is no best time of day: Mounjaro works the same morning or evening, with or without food. What matters is the same day each week.¹

Pick a day and time you will remember. Many people choose a weekend morning so early side effects fall on days off.¹ Then build a habit around it:

• Set a repeating phone alarm with the label "Mounjaro".
• Keep the pen where you will see it when you open the fridge, but always stored correctly.
• Log each injection in the GLPTrackr app so you can check the date at a glance.
• Rotate the injection site each time and note it with the date.
• Take extra care when travelling, when routines change most.

If you travel, pens go in hand luggage, ideally in a cool bag with the prescription label or a copy of your prescription. In-use pens tolerate up to 30 days not above 30°C, so most holidays need no special arrangements.¹

Our ongoing monthly clinical reviews are another safety net. If forgetting is becoming a pattern, tell your prescriber, who can help you adjust the routine within the licence. For a wider overview of support, visit our weight loss clinic.

09 · Serious side effects

Serious side effects: when to get help straight away

Serious side effects are uncommon but need urgent attention. Seek immediate medical help for: severe, persistent stomach pain that may spread to your back, with or without vomiting (possible pancreatitis); pain in the upper right abdomen, fever or yellowing of skin/eyes (possible gallbladder problems); or signs of a severe allergic reaction such as swelling of the face or throat and difficulty breathing. If you take insulin or a sulfonylurea alongside Mounjaro, watch for low blood sugar (shakiness, sweating, confusion) — your prescriber may need to adjust those medicines.¹

10 · When to speak to someone

When to contact your prescriber or pharmacy

Contact your prescriber if you are unsure what to do, whatever the timing. Contact them in particular if you have missed more than one injection or if you cannot work out the date of your last dose.

Also speak to them if you are on other medicines. Insulin or sulfonylureas, for instance, may need their doses adjusting when your Mounjaro routine changes, because of the risk of low blood sugar.¹ Oral contraceptives can be less well absorbed because Mounjaro slows stomach emptying.⁷ The SmPC advises switching to a non-oral method, or adding a barrier method (such as condoms), for 4 weeks after starting Mounjaro and for 4 weeks after each dose increase.¹

Our support team is available Monday to Friday, 9am to 5pm, by email at support@everydaymeds.co.uk, through account portal chat, or by phone on 0333 207 0413. If you think you have had a side effect, you can report it via the Yellow Card scheme.¹⁹

Mounjaro (tirzepatide) is a prescription-only medicine, supplied only after an online consultation reviewed by a GPhC-registered prescriber, and this page is information, not a substitute for medical advice.