How Many Units of Mounjaro? Dose Guide (October 2026)

01 · The short answer

Mounjaro is measured in mg, not units

The honest answer to "how many units of Mounjaro" is that there is no unit figure to find. Mounjaro (tirzepatide) comes as a pre-filled multi-dose KwikPen in six strengths: 2.5mg, 5mg, 7.5mg, 10mg, 12.5mg and 15mg.¹ Each strength is a dose in milligrams, and that is the language your prescriber, your label and the patient leaflet all use.

The pen is set by turning the dose knob until the dose indicator shows the correct dose in the window. You confirm the dose by the number in the window, never by counting clicks.¹³ The pen will not let you dial past the medicine left inside. So you are never asked to work out a volume, read a syringe barrel or turn milligrams into units.

02 · Where the confusion starts

Where the "units" idea comes from

Units are the scale printed on insulin syringes. Insulin is prescribed in units, so people moving from insulin, or reading forum threads written by insulin users, assume every injectable works the same way. It does not.

A second source is non-UK or unlicensed products sold as vials, where the seller tells you to draw liquid into a syringe and gives you a unit count. That is a different product with a different concentration and no KwikPen dial. Numbers from those threads do not transfer to a UK-licensed pen.

The same applies to specific figures you may have seen, such as a particular number of units said to equal a particular dose. Each one depends on assumptions about the syringe and the liquid that the KwikPen does not make. Treat them with caution, and if one conflicts with your label, follow your label and ask your prescriber.

03 · What to do

What to do instead of converting

Read the strength on your prescription label, then dial the pen until that number shows in the window. That is the whole job. If you are not sure which strength you should be on, your prescriber sets it, and our guide to Mounjaro dosage in units walks through what each strength looks like in practice.

A first 2.5mg pen costs £129.99 with code FIRST40 (standard price £169.99). The consultation is free and is reviewed by a GPhC-registered prescriber.

04 · Doses and the pen

The dose ladder in mg

Everyone starts Mounjaro on 2.5mg once a week. This 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 a minimum of 4-week intervals (7.5mg, 10mg, 12.5mg) up to a maximum of 15mg weekly, depending on how you respond and tolerate it.¹¹¹

Many people settle at a maintenance dose of 5mg, 10mg or 15mg. Higher is not automatically better, and your prescriber will guide the right pace.¹¹ The maximum is 15mg weekly, and that ceiling is a dose in mg, which is why a "maximum units" figure has no official meaning for this medicine.

Specific strengths have their own pages if you want the detail: how many units is 12.5 mg of Mounjaro, 15 mg of Mounjaro is how many units and 7.5 mounjaro in units. For anyone about to begin, how many units of tirzepatide to start explains the 2.5mg starting step.

05 · Using the dial

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. You confirm the dose by the number in the window, never by counting clicks.¹³ People often ask how many clicks the pen makes, and the answer is that the click count is not the measure. Follow the pen's own instructions and trust the window.

Each pen contains four weekly doses. The pen will not let you dial past the medicine left inside. If the window will not turn to a full dose, the pen does not contain enough for one and should not be used for a partial injection.¹³

Mounjaro is injected under the skin (subcutaneously) once a week, on the same day each week, at any time of day, with or without food. Licensed injection 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.¹

06 · Timing and missed doses

Timing, missed doses and changing day

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. Pick a day and time you will remember, and many people choose a weekend morning so early side effects fall on days off.¹

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

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 None of these rules involves units. They all concern the timing of a dose that the pen has already measured for you.

07 · Storage and travel

Storage and how long a pen lasts

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, which is useful for short trips, after which it should be discarded.¹ Keep the pen cap on to protect it from light, and never use a pen that has been frozen.

Because each pen holds four weekly doses, a pen normally lasts a month of weekly use. Throw the pen away 30 days after first use, or sooner if it has been above 30°C. Do not try to squeeze out an extra dose.

You can fly with Mounjaro. Carry pens in hand luggage (hold luggage can fall below freezing), ideally in a cool bag with the prescription label or a copy of your prescription. Unopened pens should be kept 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 · Pace of results

Dose and results: what to expect

People sometimes ask about units hoping to find a way to speed things up. 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. Trials measured results at 72 weeks, so think in months, not days.²

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. These are trial averages. Individual results vary, and treatment works alongside a reduced-calorie diet and increased physical activity, not instead of them.²

Treatment 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.¹¹ Any adjustment is a decision for the prescriber within the licensed ladder.

09 · 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 If you cannot keep fluids down, contact your clinical team, because dehydration needs medical help straight away.

10 · Getting it on the NHS or privately

NHS and private routes

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.

Whichever route you take, your prescriber sets the strength in mg and the pen does the measuring. Our weight loss clinic explains how a consultation, review and delivery work. Mounjaro (tirzepatide) is a prescription-only medicine, supplied only after an online consultation reviewed by a GPhC-registered prescriber (GPhC 9012878). 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.