How to Get 5mg Out of a 15mg Mounjaro Pen: What You Can Safely Do (October 2026)

01 · The decision

The short answer: order the strength you need

The only safe way to inject 5mg of Mounjaro is to use a 5mg pen. A 15mg pen is made for the 15mg dose. Its dial, its dose window and its four-dose design all assume you are injecting the strength printed on the pen.¹ That is why dividing it is not a matter of simple maths for a person at home.

Altering doses outside the licence means unknown dosing accuracy and no safety data.¹

02 · Your options

What to do instead, depending on your situation

Whichever row fits you, the answer is the same: change the pen, not the pen's contents. Our 5mg Mounjaro prescription guide covers how that works.

03 · Ordering

How ordering the right strength works

Ordering is simple and there is no charge to start. The consultation is free, and the price shown is the price paid.

• Free online consultation. A short health questionnaire with no obligation. Start your free consultation.
• Prescriber review. A GPhC-registered prescriber reviews your answers. Payment is taken when you place the order; if the prescriber decides the treatment is not suitable, the order is refunded automatically in full.
• Dispatch and delivery. We dispense and dispatch the same day when ordered by 3pm, with free next-day tracked delivery in temperature-controlled packaging. Saturday delivery is £14.99.

Pens come from official LillyDirect supply, direct from Eli Lilly's UK distribution. Every order includes needles, a sharps bin and injection guidance. All six doses are in stock. A new customer saves £40 on their first order with code FIRST40, and an automatic £25 reorder discount applies to every future order (code DOSE25).

04 · How the pen dial works

How the KwikPen dial actually works

The Mounjaro KwikPen is set by turning the dose knob until the dose indicator shows the correct dose in the window. This is the single most important fact for anyone wondering how many clicks make 5mg.

Each pen contains four weekly doses.

It follows that a 15mg pen is a 15mg tool. The number you see in the window is a dose of the strength printed on that pen. There is no setting that turns a 15mg pen into a 5mg pen.

Your own routine should be simple. Check the label and the strength on the pen. Follow the instructions in the patient information leaflet. Set the dose until the window shows the correct number, and inject under the skin once a week. If anything looks wrong, such as a window that will not turn to your dose, stop and contact the pharmacy rather than improvising.

If you want to see how strengths compare across the range, our guide to every Mounjaro pen strength sets out the doses side by side. For the specific question of clicks on the top dose, see our 15mg clicks explainer.

05 · Why a 15mg pen can't be split

Why a 15mg pen cannot be split into 5mg doses

A 15mg pen cannot be split into 5mg doses because the pen is designed to deliver the strength on its label, not fractions of it.

Altering doses means unknown dosing accuracy and no safety data.

"Can I take half of a 5mg dose?" is a related question. The licensed ladder uses specific steps, 2.5mg, 5mg, 7.5mg, 10mg, 12.5mg and 15mg, each with its own pen.¹ If a step feels too large, the answer is to talk to your prescriber about holding a dose longer or stepping down within the licence, not to halve a pen's dose.

Our page on getting medicine out of a Mounjaro pen sets out the same safety position for other versions of the question. The related guides on a 10mg pen and a 5mg pen reach the same conclusion for those strengths.

06 · Needing a lower dose

If you need a lower dose than 15mg

Higher is not automatically better. Many people settle at a maintenance dose of 5mg, 10mg or 15mg, depending on how they respond and tolerate treatment.¹¹

The licensed ladder begins at 2.5mg once a week for everyone. That starting dose is about letting your body adjust, not about weight loss itself. After at least 4 weeks the dose increases to 5mg, and can then step up by 2.5mg at minimum 4-week intervals, through 7.5mg, 10mg and 12.5mg, up to a maximum of 15mg weekly, depending on response and tolerability.¹ Your prescriber guides the pace.

That is a clinical decision, made with your history and current medicines in view. It is a very different thing from improvising with a pen at home.

Some people end up with a higher-strength pen because of how they ordered, or because they moved provider mid-treatment. That happens, and the fix is to speak to the pharmacy and ask for the right strength. Our weight loss treatments overview shows the wider options, and consultations are free, so asking costs nothing.

At the standard price a 5mg pen is £218.99 and a 15mg pen is £329.99. A new customer's first order is £40 less at any dose, and every later order is £25 off the standard price. Switching to us at 15mg? Your first order is £289.99, a first-order price.

07 · Syringes and the pen

Syringes, "leftover" liquid and the pen

Mounjaro comes as a pre-filled KwikPen, and the patient leaflet describes injecting with the pen itself.¹³

With altered administration, dosing accuracy is unknown and there is no safety data.¹

There is also a sourcing risk. The MHRA publishes counterfeit medicine alerts and runs the Yellow Card scheme for reporting problems.⁷ Anyone offering Mounjaro "in vials", "by the dose" or without a consultation or prescription is outside the regulated supply chain. Our pens come from official LillyDirect supply, direct from Eli Lilly's UK distribution, and are genuine KwikPens.

What if you have a pen that seems to have medicine left in it? Do not try to recover the remainder. Contact the pharmacy for advice. Our page on what to do with a pen remainder goes through the situation step by step.

If you have side effects or anything unexpected after an injection, tell your prescriber and report it through the Yellow Card scheme. Reporting helps regulators spot problems early, and it is open to patients as well as professionals.

08 · Storage and the 30-day limit

Storage and the 30-day in-use limit

Once a Mounjaro pen is in use, it can be kept out of the fridge not above 30°C for up to 30 days, after which it should be discarded.¹ Beyond 30 days, sterility and potency are no longer assured.

Keep pens in a fridge at 2–8°C and never freeze them. Keep the pen cap on to protect it from light, and never use a pen that has been frozen.¹³ Unopened pens should stay in the fridge until first use, and they 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. Figures circulating online often come from other countries' labels, which is a trap worth knowing about. UK pens follow the UK product information.

Travelling is straightforward if you plan. You can fly with Mounjaro. Carry pens in hand luggage, because hold luggage can fall below freezing, ideally in a cool bag with the prescription label or a copy of your prescription. In-use pens tolerate up to 30 days not above 30°C, so most holidays need no special arrangements. For hot climates use an insulated pouch, and check the destination's rules for travelling with prescription injectables before you fly.¹³

Our delivery uses discreet, temperature-controlled packaging with free next-day tracked delivery, so your pen arrives in good condition. Put it in the fridge on arrival unless you are about to use it.

09 · Missed doses and injection day

Missed doses, changing day and why you shouldn't compensate

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. 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

Dose confusion often starts with a missed injection. Someone misses a week, panics, and wonders whether a smaller top-up or a double dose from a higher pen would help. It would not. The rule is clear, and nothing in it involves a partial or catch-up dose from a different strength.

You can 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 that suits your routine. There is no best time of day: Mounjaro works the same morning or evening, with or without food. What matters is the same day each week, and many people choose a weekend morning so that early side effects fall on days off.

Injection technique is also standard. Mounjaro is injected under the skin once a week. Licensed sites are the stomach area at least 5cm from the belly button, the front of the thigh, or the back of the upper arm if someone else gives the injection. Rotate the site with each dose.¹³ Follow the pen's instructions for how to deliver the injection.

If you restart after a gap or have lost track of which strength you should be on, do not guess. Your prescriber will decide where on the ladder you should restart. Tirzepatide has a half-life of about five days, so after a final dose it takes roughly 4–5 weeks to clear the system, with nothing needing to be done while it clears.¹

Our aftercare includes ongoing monthly reviews, dose-titration and follow-up assessments by the prescribing team, plus side-effect support. Repeat orders re-check suitability, and there is no auto-shipping. If you are unsure which dose is right, that review is the place to ask.

10 · What each dose delivers

What results look like at 5mg versus 15mg

In the SURMOUNT-1 trial of 2,539 adults, people taking tirzepatide alongside diet and exercise lost on average 15% of their body weight on 5mg, 19.5% on 10mg and 20.9% on 15mg over 72 weeks, compared with 3.1% with lifestyle changes alone.² These are trial averages. Individual results vary, and treatment works alongside a reduced-calorie diet and increased physical activity, not instead of them.

Looked at another way, 85% of participants on 5mg, 89% on 10mg and 91% on 15mg had lost at least 5% of their body weight at 72 weeks. Half of participants on 10mg and 57% on 15mg lost at least 20%.² For someone starting at 100 kg, 15% is about 15 kg and 20.9% is about 21 kg.

Why does that matter here? Because it shows 5mg is a genuine, effective maintenance dose and not a lesser option. Many people settle at 5mg, 10mg or 15mg, and your prescriber guides the right pace.¹¹ If you are tempted to improvise a 5mg dose because you think 15mg is "too much" or 5mg is "too little", the better step is a proper dose review.

Pace matters too. Weight loss on Mounjaro is gradual by design. The first weeks on 2.5mg are an adjustment phase and losses are usually modest. Most measurable progress builds from 5mg onward, month by month. Think in months, not days, and judge progress by trend rather than individual weigh-ins.²

Response is reviewed by your prescriber. If you have lost less than 5% of your starting weight after 6 months on the highest dose you can tolerate, your prescriber will discuss whether continuing or stopping is right for you. Early on, mild nausea, altered appetite and tiredness in the first days after each injection are the commonest effects and usually settle.

None of this predicts your own result, because trial averages do not.

11 · 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

12 · NHS and private access

NHS and private routes to the right dose

Mounjaro is available on the NHS, but access is being phased in over several years. NICE recommends it for adults with a BMI of at least 35 plus at least one weight-related condition, and the NHS primary-care rollout began in June 2025 with the highest-need groups first, initially BMI 40+ with four or more qualifying conditions.⁴⁶ Full rollout is expected to take years, which is why many people who meet the licensed criteria choose regulated private treatment rather than waiting.

If you are on NHS treatment, your dose changes are managed by your NHS prescriber, and the same rule applies: ask them rather than altering a pen yourself. The NHS guide to tirzepatide covers the medicine in general terms.⁵

Privately, Mounjaro is licensed for weight management in adults with a BMI of 30 or above, or a BMI between 27 and 30 with at least one weight-related condition such as high blood pressure, high cholesterol, obstructive sleep apnoea, cardiovascular disease, prediabetes or type 2 diabetes. It must be used alongside a reduced-calorie diet and increased physical activity. A prescriber assesses your BMI, medical history and current medicines before deciding whether it is suitable.¹

Across the UK pharmacies we track (checked 10 October 2026), Mounjaro pens run from £143.96 to £339.00 per month depending on dose and provider. For the same dose, the gap between providers ranges from £27 to £41.

Our service is a full UK online pharmacy, GPhC-registered (9012878). Our free consultation is reviewed by a GPhC-registered prescriber, and payment options include Visa, Mastercard, Klarna and pay-monthly options, with no subscriptions. A new customer's first order is £40 less, and every later order £25 less.

Support runs Monday to Friday, 9am to 5pm, by email at support@everydaymeds.co.uk, account portal chat or phone on 0333 207 0413. The free GLPTrackr app helps you track your journey.