Can you use the last dose of Mounjaro?

Is the last dose in a Mounjaro pen a full dose?

It is. Eli Lilly designs the KwikPen so that each of the four doses contains the same volume of tirzepatide solution. The pen does not reduce the amount it delivers as it empties, and there is no technical reason the fourth injection would be weaker, smaller, or less effective than the earlier three.

One misconception worth clearing up gently: some people notice a small amount of liquid left in the pen after the final click and assume they have missed part of their dose. You have not. A little residual fluid in the barrel is intentional — it ensures the plunger mechanism can fully expel dose four without air entering the needle. The pen has delivered what it should. You can read more about whether there is an extra dose in a Mounjaro pen if you want the full detail on how the pen counts its doses.

The Mounjaro overview page explains how tirzepatide works as a dual GIP and GLP-1 receptor agonist, and why each weekly dose matters for maintaining steady levels in the body.

What should you do after the last dose?

Once you have used dose four, the pen is finished. The KwikPen locks automatically after the last dose, you may notice the plunger will not depress again, which is normal and designed to prevent accidental double-dosing. Do not try to use any droplets visible in the barrel; they are not a clinically extractable dose.

Your next step is straightforward: your following injection is due one week later, using a new pen at whatever strength your prescriber has set for you. If you are between pens and your supply has not arrived yet, contact your prescriber or pharmacy before skipping or delaying a dose rather than guessing, timing gaps can affect how your body adjusts to treatment. If you are wondering about the mechanics when a pen seems stuck, there is useful guidance on what to do if your Mounjaro pen is stuck on the last dose.

Used pens should go straight into a sharps disposal container. If you do not already have one, a sharps container is the correct way to dispose of used injector pens in the UK.

Does your dose change after the last pen at a given strength?

This is a prescriber decision, not something you should change yourself. Mounjaro is licensed in UK strengths from 2.5 mg through to 15 mg, and treatment typically moves upward in 4-week (one-pen) steps when the prescriber judges it appropriate. The starting dose exists primarily to help your system adjust, the therapeutic work builds from there.

At nume (at our pharmacy) a GPhC-registered Independent Prescriber reviews your case before every repeat order. That review considers whether your current dose is right, whether a step up is clinically suitable, and whether there are any reasons to pause. You do not decide the next dose; the prescriber does, based on your weight, tolerance and progress. Details on how each strength works in practice are on the Mounjaro 5 mg page for that tier, or you can look at the broader weight-loss treatment overview for context across options.

If you are wondering whether staying on a lower strength long-term is right for you, there is dedicated guidance on staying on the lowest Mounjaro dose. Worth reading before assuming you need to move up.

Where does the cost picture sit once you reach the last dose?

Each Mounjaro pen covers four weeks of treatment, so every pen you use is one month's supply. The cost per pen varies by dose strength, and since Eli Lilly revised UK list prices in September 2025, private prices across providers have generally ranged roughly £149–£375 per month depending on dose and clinic, as widely reported. The Mounjaro price page sets out the full context of what those figures include and exclude, consultation fees, prescription charges, delivery, and aftercare vary considerably between services.

At nume, one transparent price covers the clinical consultation, prescription, the pen itself, and free next-working-day tracked delivery. No subscription, no auto-renewal; every repeat is reviewed by a prescriber before dispatch. That structure means finishing a pen is a natural point at which your suitability for the next one is confirmed, not assumed. The NHS tirzepatide page has further background on how tirzepatide works and what to expect across the course of treatment.

If you have questions about your treatment or want to get started with a clinical assessment, you can start your free consultation with our prescribers today.