Can You Get 5 Weeks Out of a Mounjaro Pen? (October 2026)

01 · The decision

Can one Mounjaro pen last five weeks?

No. Each Mounjaro KwikPen contains four weekly doses, and the licensed way to use it is one injection a week for four weeks.¹ The pen is built around that number. When it has delivered four doses, it has done its job and should be discarded safely.

People ask about a fifth week for understandable reasons: a little liquid is visible in the pen, the pens are not cheap, or a missed dose has thrown the calendar out. None of these turns a four-dose pen into a five-dose pen.

02 · What to do

What to do instead of stretching a pen

The answer depends on why you are asking. This table matches the common situations to the sensible next step.

If you want a deeper look at the leftover-liquid question, our guide on what the remainder in a pen means covers the same ground from another angle. Our guide to the last dose in a pen explains how to make sure your fourth injection is a full one.

03 · Cost

What a pen costs, and how to plan the year

Every Mounjaro pen we supply contains four weekly doses. Your first 2.5mg pen costs £129.99 with code FIRST40 (standard price £169.99). The standard price of one pen at each dose is £169.99 at 2.5mg, £218.99 at 5mg, £279.99 at 7.5mg, £290.99 at 10mg, £319.99 at 12.5mg and £329.99 at 15mg. All six doses are in stock.

A new customer gets £40 off their first order at any dose, including people switching to us at a higher dose. Switching at 15mg? Your first order is £289.99. After that, every later order is £25 off the standard price, with code DOSE25.

If you step up after 4 weeks on each dose, your first four pens (2.5mg to 10mg) cost £959.96 at standard prices. A first year of 52 weeks is 13 pens and costs £2,711.88 if you settle at 5mg, up to £3,599.88 at 15mg. Those totals are before discounts, so a new customer's first order is £40 less and every later order £25 less. At other maintenance doses, use that dose's monthly price.

Across the UK pharmacies we track, Mounjaro pen prices run from £143.96 to £339.00 per month depending on dose and provider (checked 10 October 2026).

04 · Ordering

How ordering works, so you never run short

Running out is the real cause of most stretching temptations, and it is avoidable. Ordering takes three steps:

• Complete the free online consultation, a short health questionnaire with no charge and no obligation.
• A GPhC-registered prescriber reviews it. Payment is taken when you place the order; if the prescriber decides the treatment is not suitable, the order is refunded automatically in full.
• We dispense and dispatch. Orders placed by 3pm go out the same day, with free next-day tracked delivery in temperature-controlled packaging.

Repeat orders re-check suitability, and there is no auto-shipping, so you decide when the next pen is sent. Order a few days before your fourth dose and the next pen arrives in good time. You can buy Mounjaro online from our official LillyDirect supply, with needles, a sharps bin and injection guidance included with every order.

05 · How the pen is built

How the KwikPen dial works

The KwikPen is set by turning the dose knob until the dose indicator shows the correct dose in the window.

By the fourth injection, the dial is the pen's own safeguard.

The patient information leaflet in the box is the authoritative guide to the pen's steps, and it is worth rereading before each new pen.¹³ Our walkthrough on how the medicine leaves the pen explains what the device does at each dose, without any workarounds.

06 · Why stretching is unsafe

Why trying for a fifth week is not safe

Altering doses outside the licence means unknown dosing accuracy and no safety data.

That covers every version of the idea: injecting what is left after four doses, splitting doses to eke out a fifth week, or opening the pen to recover liquid.

07 · Storage and the 30-day limit

Storage, and how the 30-day limit fits in

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, and never use a pen that has been frozen.

Four weekly doses fit comfortably inside that 30-day window, which is another reason the pen is a four-week unit. If you travel, in-use pens tolerate up to 30 days not above 30°C, so most holidays need no special arrangements.¹

Unopened pens belong in the fridge and keep until the expiry date printed on the box. If an unopened pen has been out of the fridge, check with the pharmacy before using it rather than relying on a remembered day limit, because figures circulating online often come from other countries' labels.¹³

08 · Missed doses and schedule slips

If a missed dose makes the pen feel out of step

A late dose does not add a week to the pen. 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

Skipping a dose means the pen simply lasts a little longer on the calendar, but it still holds four doses, and it still must not be used beyond 30 days, or above 30°C out of the fridge once in use. If a skipped dose leaves you unsure whether the pen is still within its use window, ask the pharmacy before your next injection.

You can also change your weekly injection day if needed, as long as at least 3 days (72 hours) have passed since your last dose.¹ Pick a day and time you will remember, since the time of day does not change how the medicine works.¹

09 · Dose ladder and pen changes

How pens and the dose ladder line up

Everyone starts on 2.5mg once a week. After at least 4 weeks the dose increases to 5mg, and can then step up by 2.5mg at a minimum of 4-week intervals (7.5mg, 10mg, 12.5mg) to a maximum of 15mg weekly, depending on response and tolerability.¹¹¹

Each strength comes in its own pen with four weekly doses, and you stay on each dose for at least 4 weeks, depending on how you respond and tolerate it.

Many people settle at 5mg, 10mg or 15mg, and higher is not automatically better. Your prescriber will guide the pace. Our guide to what happens to the rest of a finished pen and the week-by-week pen dose timeline show how this works in practice.

10 · Week five and expectations

If your question is really about week five of treatment

By week five you have finished the first 2.5mg pen, and after at least 4 weeks the dose increases to 5mg.¹ The starting dose is about letting your body adjust, not about weight loss itself.

Experiences differ widely in the early weeks. Some people notice appetite change and early loss in week one, others feel little until a higher dose, and both are normal. Mild nausea, altered appetite and tiredness in the first days after each injection are the commonest early effects and usually settle.

Weight loss on Mounjaro is gradual by design. Trials measured results at 72 weeks, so think in months, not days. In SURMOUNT-1, adults lost on average 15% of body weight on 5mg, 19.5% on 10mg and 20.9% on 15mg over 72 weeks, against 3.1% with lifestyle changes alone. These are trial averages and individual results vary.² If you are at this stage, see our pages on five weeks on Mounjaro and on no weight loss at five weeks.

11 · Disposal and safety

Finishing a pen safely

When the fourth dose is done, the pen is finished. Put the needle and pen into the sharps bin included with your order, and do not reuse needles. Our guide on removing the needle from a pen covers that step.

If you notice anything unexpected with a pen, such as a dial that will not turn or damage, speak to your prescriber or pharmacist; tell them about any new or lasting symptom after an injection. Side effects can be reported through the MHRA Yellow Card scheme.¹⁹

Our support team is available Monday to Friday, 9am to 5pm, by email at support@everydaymeds.co.uk, account portal chat, or phone on 0333 207 0413. Ongoing monthly reviews, dose-titration and side-effect support from the prescribing team are included, so questions about pens and doses have a proper place to go.

Mounjaro (tirzepatide) is a prescription-only medicine, supplied only after an online consultation reviewed by a GPhC-registered prescriber. It is used alongside a reduced-calorie diet and increased physical activity. Individual results vary. This page is information, not a substitute for medical advice.

12 · 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