How long does 10mg of tirzepatide last — and what that means for your treatment

One pen lasts four weeks, here's why that matters at 10mg specifically

The 10mg Mounjaro KwikPen is pre-filled and designed for once-weekly subcutaneous injections. Four injections per pen, one pen per month. That arithmetic is the same at every strength, from 2.5mg all the way to 15mg. What changes at 10mg is context: by the time you reach this dose, you have typically been on tirzepatide for at least three months, your body has had time to adjust to the medicine, and both you and your prescriber have data on how you're responding.

One misconception worth clearing up gently: some people assume the higher the dose, the faster the pen runs out. It doesn't work that way. The volume of each injection varies slightly across strengths, but the cadence (one injection per week, four per pen) stays fixed regardless of whether you're on 2.5mg or 15mg. If you're curious about how long a 2.5mg Mounjaro pen lasts and how that compares to later doses, the answer might surprise you. A pen at 5mg lasts the same four weeks as one at 10mg.

What can shorten your supply in practice is an injection error: too much medication drawn out, a pen used on the wrong setting, or a failed injection that you're unsure got a full dose. If you have any doubt about a dose you've taken, the right call is to contact your prescriber rather than compensate with an extra injection. The NHS tirzepatide medicines page covers missed and uncertain doses clearly.

Where 10mg sits in the titration schedule, and the decision your prescriber makes

Tirzepatide starts at 2.5mg, a dose that exists to let your system settle rather than to drive weight loss. From there, the schedule typically steps upward every four weeks: 2.5mg, 5mg, 7.5mg, 10mg. So 10mg is usually reached around the four-month mark, assuming the earlier doses were tolerated without a reason to pause. Some people stay at an earlier dose longer if side effects have been significant; others may move through more quickly if their prescriber judges it clinically appropriate.

At 10mg you are in the upper half of the licensed range. The two remaining steps above are 12.5mg and 15mg. Whether you move to one of them, or whether 10mg becomes your maintenance dose, is a clinical decision, not a preset outcome. Your prescriber will look at your weight trajectory, your experience of side effects, and any health changes since your last review. For a detailed breakdown of what tirzepatide 10mg involves at this stage of treatment, our 10mg tirzepatide dosage guide covers the clinical picture in full.

NICE's appraisal of tirzepatide, TA1026, notes that if less than five per cent of body weight has been lost after six months at the highest tolerated dose, continuing treatment should be reviewed. That review applies regardless of which dose you've reached, including 10mg as a maintenance dose.

What happens around the time your 10mg pen runs out

Because tirzepatide has a half-life of roughly five days, its concentration in your blood drops steadily if your next dose is delayed. The effects on appetite and gastric emptying don't switch off the moment a pen runs out, but they do fade. Some people notice hunger returning or food feeling less satiating in the days before their next pen arrives, particularly if there's a gap between finishing one pen and starting the next.

Planning ahead matters more at this stage of treatment than it did at the beginning. Running out with no replacement ordered, no prescriber review completed and no pen on its way is the situation most worth avoiding. If you're weighing up how private treatment works around dose reviews and repeat orders, what happens around your last dose walks through the practical side.

At nume (sorry, at our pharmacy) every repeat order goes through a clinical re-review before it's dispensed. There are no automatic renewals. That process is deliberate: it gives your prescriber a checkpoint at each pen, which is exactly what the NHS England guidance on weight management injections recommends as good clinical practice. If cost and what's included in a repeat prescription are on your mind, our treatment page sets out what's covered.

Storage and the end of your pen, practical points for 10mg users

Mounjaro pens are stored in the fridge at 2–8°C. There is a limited window for room-temperature storage once a pen has been removed from the fridge; the exact duration is stated in the Patient Information Leaflet and the Mounjaro SmPC on the eMC, not something to guess at, because it varies and getting it wrong risks using a compromised medicine. Keep the pen in its original packaging until you're ready to use it, and don't freeze it.

The pen locks after the fourth injection, which is useful confirmation that the supply is genuinely finished. If your pen locks before you've completed all four doses, or after what feels like fewer than four injections, contact your prescriber and pharmacy rather than opening a new pen early without guidance. Injection technique can occasionally mean a full dose isn't delivered, guidance on 10mg tirzepatide injection technique is worth reviewing if you have any uncertainty about how to use the pen correctly.

When you're ready to explore treatment or check your eligibility, speak to our prescribers through a free consultation, they review your information the same day and can advise on the right dose for where you are in treatment.