One missed weekly dose
The product information says you can take a missed dose as soon as possible within four days of when it was due. If more than four days have passed, skip that dose and take the next one on your usual day. Never take a double dose to make up for a missed one.
Count the gap using the real dates and times. The test is how long since the dose was due, whatever the calendar week says. If you are unsure where the four-day limit falls, ask a pharmacist before you inject.
Changing your injection day
The label lets you move your weekly injection day as long as there are at least three days between doses. This rule covers a one-off change of day. You still inject once a week after the switch, never every three days.
Write the dates on a calendar if a missed dose and a new injection day fall close together. Record what you injected and when, and update the record whenever you move a reminder. Take extra care if someone else helps with your injections.
Restarting after a longer gap
The single missed-dose rule does not tell you how to restart after several missed weeks. Your prescriber will look at how long you stopped, your last strength, how well you coped with it, your current health and why you stopped. Going straight back to a higher dose you used to manage may not suit you after a long break.
Tell them whether the break followed illness, surgery, pregnancy concerns, side effects, cost or a supply problem. The reason often matters as much as the number of days. A new provider needs your full history, beyond the strength on your last order.
If you are unsure the injection worked
Doubt about an injection is different from a confirmed missed dose. Repeating it risks giving you too much medicine. If the pen failed, leaked or you are unsure about the timing, follow the device instructions and contact the pharmacist who supplied it or your prescribing team.
Keep the pen and its packaging stored safely so you have them when you talk to the pharmacist. Describe what happened step by step. Appetite, side effects and the amount of liquid you can see are no reliable guide to how much medicine you received.
Avoiding the next missed dose
Pick a reminder system where you tick off each dose, since a phone alarm disappears once dismissed. Check your supplies and prescription review dates early so a gap does not catch you out. If shift work or travel makes weekly timing hard, agree a workable schedule with your prescriber.
Illness needs its own advice, especially with vomiting, dehydration or suspected pancreatitis. If a clinician has told you to stop and get checked, do not use the four-day rule to inject anyway. If you have diabetes, also follow your agreed glucose monitoring and sick day plan.
Sources
Your own medicine leaflet and prescriber come first. A source from another country does not mean the same rule applies in the UK.
- Mounjaro UK Summary of Product Characteristics, updated September 2026 medicines.org.uk
- Mounjaro UK patient information leaflet medicines.org.uk
- NICE: prescribing, reviewing and stopping tirzepatide nice.org.uk
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