Dosing & Usage

Missed Dose Guide

Forgot your weight loss injection? Learn what to do if you miss a Mounjaro or Wegovy dose, including when to take it and when to skip.

Whether you forgot your Mounjaro or Wegovy injection, missed it because you were ill, or knew it was coming and want to plan ahead, this guide explains the rules for managing missed doses. Mounjaro and Wegovy have different missed-dose windows because they have different pharmacokinetic profiles — getting the wrong rule for the wrong medicine can mean either an unnecessary skip or an unsafe double dose. LetsLoseWeight is an independent comparison site; we do not prescribe medication, and your prescriber's specific advice takes precedence.

The headline rules

Medicine Late by less than this Action Late by more than this Action
Mounjaro (tirzepatide) 4 days (96 hours) Take the missed dose now More than 4 days Skip and take next dose on schedule
Wegovy (semaglutide) 2 days (48 hours) Take the missed dose now More than 2 days Skip and take next dose on schedule

The difference is built into the licensed advice in the Mounjaro SmPC and Wegovy SmPC. It reflects how long each medicine stays meaningfully active in the body.

Mounjaro — the 96-hour rule

If you miss a Mounjaro dose:

  • Within 4 days of when it was due — take it as soon as you remember, then resume your normal weekly schedule. Your next dose is still 7 days after your usual day.
  • More than 4 days late — skip the missed dose entirely. Take the next dose on your normal schedule.

If you miss the dose by 5+ days and skip it, you will have a longer gap (up to 14 days) between doses. This is acceptable but not ideal — your appetite-suppressing effect may dip in the second half of that gap, and side effects can return when you resume.

Wegovy — the 48-hour rule

If you miss a Wegovy dose:

  • Within 2 days of when it was due — take it as soon as you remember, then resume your normal weekly schedule.
  • More than 2 days late — skip the missed dose entirely. Take the next dose on your normal schedule.

If you skip a dose, the next dose should be at least 3 days after the day you would have taken the missed one, then continue on the normal weekly schedule from there.

The shorter window for Wegovy reflects semaglutide's faster offset compared with tirzepatide.

What happens if you miss two or more in a row

Missing a single dose is a routine situation handled by the rules above. Missing two or more consecutive doses is different — your body will have largely lost the active effect of the medicine, and resuming at the same dose can trigger nausea and other side effects similar to your first weeks on it.

If you miss two or more consecutive doses:

  • Contact your prescriber before your next injection. They will usually advise.
  • Most prescribers will recommend dropping back a dose level — particularly if you have been on a higher dose. The standard fallback is to drop to the previous step you tolerated.
  • Some will recommend restarting the titration more cautiously if a longer break (4+ weeks) has occurred. See our restarting guide.

The cautious approach exists because the slow titration is what protected you from severe side effects in the first place. Restarting at full maintenance dose after a break can produce nausea and gastrointestinal upset comparable to your first weeks on the medicine.

When to take a "late" dose

A few practical rules within the missed-dose window:

Don't take two doses on the same day

If you remember on the morning of your next scheduled dose that you missed last week's, do not take both. Skip last week's, take this week's, continue on schedule.

If less than 3 days remain until your next dose, skip the missed one

For Wegovy specifically, if you remember a missed dose 5 days late but your next dose is due in 2 days, skip the missed one. There must be at least 3 days between the make-up dose and the next scheduled dose.

For Mounjaro the equivalent rule is to ensure at least 3 days between doses.

Don't double up to "catch up"

Taking two doses close together to make up for a missed one significantly increases the risk of severe side effects without any improvement in long-term weight loss. The licensed advice never permits this.

Permanently changing your injection day

If you frequently forget on your current day or want to change it for practical reasons (e.g. moving from Saturday to Wednesday), the licensed approach is:

  • Take your normal dose on your current day
  • At least 3 days later, take your dose on the new day — provided you are within the missed-dose window above
  • Continue weekly on the new day

This effectively uses one "early" dose to shift the schedule. The minimum gap between any two doses must be 3 days regardless of medicine.

If your current and target days are close together (e.g. moving from Sunday to Wednesday — only 3 days apart, going forward), this works directly.

Special cases

You missed the dose because you were unwell

If you skipped because of severe gastrointestinal illness (vomiting, diarrhoea), unrelated severe illness, surgery, or any reason where the prescriber would normally pause treatment — talk to them before resuming, especially if the gap has been more than a week.

You're going on holiday and worried about timing

Both medicines allow flexibility. Plan your dosing day around your travel:

  • Inject the day before you fly so you don't have to handle a temperature-sensitive pen on the plane
  • Pack a spare pen in case of delay or breakage
  • Use a temperature-controlled travel bag if you'll be away longer than 21 days (Mounjaro) or 28 days (Wegovy)

If you cross multiple time zones for a long trip, choose a stable day in the new time zone — the medicine doesn't need to be on the same UK clock time.

You're switching between Mounjaro and Wegovy

Switching is not a missed-dose situation — it's a treatment change requiring a washout. Stop the first medicine, wait the recommended interval (around 5 weeks for Wegovy → Mounjaro), then start the new one at its standard starter dose. See our switching guide.

You missed the dose by more than 2 weeks

This counts as a treatment break, not a missed dose. Don't restart at the same dose. Contact your prescriber — they will likely advise dropping back a level or restarting titration. See our restarting guide.

What to expect after a missed-dose make-up

If you take a make-up dose within the missed-dose window:

  • Side effects may be slightly more noticeable in the day or two after — particularly nausea — because the gap before this dose was a bit longer than usual
  • Your blood sugar (if you have diabetes) may have been slightly higher during the gap — check more frequently for a few days
  • Your weight loss trajectory should be unaffected — a single late dose does not meaningfully change long-term outcomes

If you skip a missed dose:

  • Side effects may return briefly when you take the next dose, since the gap is longer
  • Appetite control may have wobbled in the second half of the gap — back to normal once the next dose takes effect
  • Long-term outcomes are unaffected by occasional skipped doses, though repeated skipping is a problem

Frequently asked questions

I'm 3 days late on Wegovy — what do I do?
That's outside the 48-hour window. Skip the missed dose, take the next on your normal day. Make sure the gap to the next dose is at least 3 days from when you remembered.

I'm 2 days late on Mounjaro — should I take it?
Yes, that's within the 96-hour window. Take it now and keep your usual day for the next one.

I missed a dose on holiday with no fridge — is the medicine still OK?
Mounjaro can be kept at room temperature (below 30°C) for up to 21 days; Wegovy for up to 28 days. If it has been within those limits and not frozen, the pen is still usable.

Can I just take a half-dose to catch up?
No. The pre-filled pens are designed to deliver a full dose only. There is no licensed way to take a partial dose.

I missed because I had a bad stomach bug. When can I restart?
Once you can keep fluids down and feel reasonably well, you can resume. If the bug lasted several days, you may be outside the missed-dose window — follow the rules above for that scenario. Talk to your prescriber if uncertain.

Will missing one dose set back my progress?
A single missed dose does not meaningfully affect long-term progress. Repeated missed doses (multiple per month) can. The biggest practical impact of one miss is the brief return of side effects when you resume.

Next steps

Sources

This guide is for general information only. Your prescriber's specific advice takes precedence. If in doubt about a missed dose, contact your prescriber or supplying pharmacy.

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Missed Dose Guide UK: Mounjaro & Wegovy Rules | LetsLoseWeight