What's the Starting Dose of Mounjaro? (October 2026)

01 · The answer

The starting dose of Mounjaro is 2.5mg once a week

Everyone starts Mounjaro on 2.5mg once a week. This starting dose is about letting your body adjust, not about weight loss itself.¹ It is the lowest of the licensed strengths, and the pen you receive for it is a multi-dose KwikPen, which means one pen covers your first month of weekly injections.

That answer is the same whether you are treating weight or type 2 diabetes, whether you have tried other injections before, and whether you are very motivated to move quickly. The licence is built around a gradual climb so your body can adjust.

If you want the same answer framed around weight loss specifically, see our guide to the Mounjaro starting dose for weight loss. If you are comparing it with other injectables, our page on the starting dose of GLP-1 medicines sets out how the ladders differ.

02 · Your decision

Is the starting dose relevant to you, and what next?

The starting dose matters to you if you are about to begin treatment for the first time, or returning after a long break. It also matters if you have been offered a higher first dose elsewhere and want to know whether that is normal. The licensed route is the same for everyone, so a first prescription should be for 2.5mg.

If you have been on Mounjaro already and are switching provider, your new prescriber will decide where you should continue. Your new prescriber will review where you are and what you tolerated before deciding. Say honestly what dose you were last taking and how long ago.

Ready to start? Your first 2.5mg pen costs £129.99 with code FIRST40 (standard price £169.99) on our Mounjaro pen page, after a free online consultation reviewed by a GPhC-registered prescriber. If you want a plain buying route for the starter pen, read how to buy the starting dose. For the wider programme around the medicine, see our weight loss clinic.

03 · Why 2.5mg first

Why Mounjaro starts at 2.5mg

Mounjaro starts at 2.5mg because the starting dose is designed for tolerability, not for results. Everyone starts Mounjaro on 2.5mg once a week, and this starting dose is about letting your body adjust.¹

Tirzepatide activates two natural gut-hormone receptors at once, GIP and GLP-1. Together these help regulate appetite, slow how quickly the stomach empties and improve the way the body responds to insulin.¹

A low first step gives your body time to adapt before the dose rises. That is why the starting dose is sometimes described as an initiation dose rather than a treatment dose.

It is also why you cannot skip it. The licensed ladder begins at 2.5mg for everyone, and your prescriber will not start you higher as a first prescription. If you see a seller offering to supply a higher first strength without a consultation or prescription, treat that as a red flag rather than a bargain.

04 · The dose ladder

The full Mounjaro dose ladder

The Mounjaro dose ladder runs from 2.5mg to a maximum of 15mg once weekly, and the pen comes in six strengths. It comes as a pre-filled multi-dose pen (KwikPen) in six strengths: 2.5mg, 5mg, 7.5mg, 10mg, 12.5mg and 15mg.¹

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.¹ Note that every four weeks is the shortest allowed gap, not a target. Your prescriber can hold you on a dose for longer.

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.¹ If you step up after 4 weeks on each of 2.5mg, 5mg, 7.5mg and 10mg, your first four pens cost £959.96 at standard prices; a new customer's first order is £40 less and every later order £25 less.

05 · Time on 2.5mg

How long you stay on 2.5mg

You stay on 2.5mg for a minimum of four weeks, which is one full pen of weekly doses. Each KwikPen contains four weekly doses.¹ So your first pen takes you through the starting phase, and the next prescription is normally for 5mg.

Four weeks is a floor, not a promise. If you are having more side effects than you can comfortably manage, your prescriber can hold you on the same strength for longer rather than stepping up on schedule. That sits within the licence, which lets the dose go up depending on how you respond and tolerate it.¹

Our ongoing monthly reviews are built around exactly this decision. Before each repeat order we recheck suitability, ask how the last month went and let the prescribing team decide whether to step up, hold or, if needed, step back down within the licence. There is no auto-shipping, so nothing arrives before someone has looked at your answers.

06 · First weeks

What the first weeks on 2.5mg feel like

The first weeks on 2.5mg are an adjustment phase, and experiences differ widely. Some people notice appetite change and early loss straight away, others feel little until a higher dose, and both are normal.¹

Mild nausea, altered appetite and tiredness in the first days after each injection are the commonest early effects and usually settle.¹³ Early loss includes water weight, so the trend over weeks matters more than any single weigh-in.

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.¹ Think in months, not days, and judge progress by trend rather than individual weigh-ins.

A practical point: many people choose a weekend morning for their injection so that early side effects fall on days off. That is a convenience choice, not a medical requirement, since Mounjaro works the same morning or evening, with or without food.¹

If a new symptom worries you, or something feels unusual and is not listed in the leaflet, tell your prescriber. You can also report suspected side effects through the MHRA Yellow Card scheme.¹⁹

07 · Injecting your first dose

How to inject your starting dose

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.¹ 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

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

Needles, a sharps bin and injection guidance come with every order, so you do not need to buy anything separately before your first injection.

Pick a day you will remember. There is no best time of day, and what matters is keeping the same day each week.¹

08 · Missed doses

Missed doses and changing your injection day

If you miss your first doses, the rule is based on how long ago the scheduled injection was. 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

You can change your weekly injection day if needed. 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 this changes the starting dose. A missed injection in your first pen does not mean restarting, and it does not mean doubling up. If you are unsure, contact us on the support line during opening hours and a member of the team will help you work out what to do.

09 · Halving and microdosing

Can you start lower than 2.5mg?

No. Everyone starts Mounjaro on 2.5mg once a week, the lowest of the six licensed strengths.

If you are worried about side effects at the first dose, the safe route is to tell the prescriber before you inject, or as soon as you notice problems. That opens up options within the licence, such as holding the dose for longer before stepping up.

10 · Starting at 5mg?

What if you are offered 5mg as a first dose?

A first prescription for Mounjaro should be 2.5mg, because that is the licensed starting dose for everyone.¹ If someone offers you 5mg or higher as a first-ever dose, ask why.

There is a legitimate reason people ask about 5mg: they are moving from another provider after already completing the early steps. In that case a prescriber looks at what you have taken, and when, then decides where you should continue. That is a continuation decision, not a new starting dose. Our page on starting on 5mg Mounjaro and the related 5mg starting dose guide explain how this works in practice.

Switching to us at a higher dose? A new customer gets £40 off their first order at any dose with code FIRST40, and every later order is £25 off the standard price (code DOSE25). Your first order at 15mg, for example, is £289.99.

11 · Results and review

What the starting dose means for results

The starting dose is the first step, not the whole treatment, so trial results describe the full dose range. 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.² Trial averages do not predict your own result.

Your response is reviewed along the way. 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.¹

12 · Storage and travel

Storing and travelling with your first pen

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 — 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.

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.¹ 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.

Your first pen arrives by free next-day tracked delivery in temperature-controlled packaging, with same-day dispatch when ordered by 3pm. For more on timings, see starting dose next-day delivery.

13 · 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 There is no proven way to prevent pancreatitis or gallbladder problems while taking Mounjaro.

14 · NHS or private

The starting dose on the NHS versus privately

The starting dose is identical on the NHS and privately, because it is set by the licence. Mounjaro is available on the NHS, but access is being phased in over several years.⁴ 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).⁶

Full rollout is expected to take years, which is why many people who meet the licensed criteria choose regulated private treatment rather than waiting.⁶ Whichever route you take, you begin on 2.5mg, move up in the same steps and are reviewed along the way.

For a deeper look at the generic drug, our page on the recommended starting dose of tirzepatide covers the ingredient rather than the brand.