Mounjaro Composition: What Is in the Pen? (October 2026)

01 · The short answer

What is Mounjaro made of?

Mounjaro is the brand name for tirzepatide, a once-weekly injectable prescription medicine made by Eli Lilly.¹ Tirzepatide is the active ingredient, meaning it is the part that produces the medicine's effect. In the UK it is licensed for weight management in adults and for type 2 diabetes.¹

Around the active ingredient sit the inactive ingredients, often called excipients. These keep the liquid stable and comfortable to inject. The authoritative version is in the electronic medicines compendium entries for the KwikPen: the Summary of Product Characteristics for clinicians, and the Patient Information Leaflet for you.¹³ Both are free to read.

If you want a deeper look at the molecule, our guides on the Mounjaro chemical structure and the Mounjaro chemical name go further. For a plain-English view of the contents of the pen, see Mounjaro injection ingredients.

02 · What it means for you

Which parts of the composition matter to a patient?

For most people, three practical points matter more than the chemistry. The first is what the medicine does in the body. The second is how strong each pen is. The third is whether anything in the pen could be a problem for you personally, such as an allergy.

On the first point, tirzepatide is the first treatment of its kind to activate two natural gut-hormone receptors at once: GIP and GLP-1.¹ Together these help regulate appetite, slow how quickly the stomach empties, and improve the way the body responds to insulin.¹

On the second, the pen comes in six strengths: 2.5mg, 5mg, 7.5mg, 10mg, 12.5mg and 15mg. Each KwikPen contains four weekly doses. The active ingredient is the same in every strength; only the amount differs.

On the third, allergies and sensitivities are a conversation for your prescriber. When you complete our free online consultation, your answers are reviewed by a GPhC-registered prescriber, and the leaflet in the box lists every ingredient for you to check yourself. If you have ever reacted to an injectable medicine, say so in the consultation.

03 · Next step

Is Mounjaro right for you?

Composition is only one part of that decision. If you meet the licensed criteria and want to look at the medicine itself, the Mounjaro pen page shows the starting pen at £169.99 for four weeks at standard price, with live stock shown as in stock. A new customer's first order is £40 less with code FIRST40, and every later order is £25 less (code DOSE25).

You can also read about the wider programme on our weight loss clinic page. Payment is taken when you place the order; if the prescriber decides the treatment is not suitable, the order is refunded automatically in full. Mounjaro is supplied only after an online consultation reviewed by a GPhC-registered prescriber. It is used alongside a reduced-calorie diet and increased physical activity, and individual results vary.

04 · At a glance

Composition quick reference

05 · Active vs inactive ingredients

Active and inactive ingredients explained

Every injectable medicine has an active ingredient and a set of inactive ingredients. In Mounjaro the active ingredient is tirzepatide.¹ It is the only component that is described as producing the treatment effect, and it is the name that appears on your prescription label alongside the brand.

The inactive ingredients do supporting jobs. In general, an injection needs something to keep it at a suitable acidity, something to make it comfortable when it enters the tissue under the skin, and something to keep the liquid stable over its shelf life. Those roles are common to many injectables. The precise substances Eli Lilly uses are listed in the leaflet that comes in the box.¹³

A practical habit helps here. When your pen arrives, read the leaflet from the box. Check the ingredients against any allergies you know about. If anything is unclear, contact the prescribing team before your first injection. Our support team is available Monday to Friday, 9am to 5pm, by email at support@everydaymeds.co.uk, through the account portal chat, or by phone on 0333 207 0413.

It is also worth knowing that Mounjaro is a prescription-only medicine. You cannot judge it as you would a food product, because the composition is controlled, tested and regulated. That is one reason we only supply it after a consultation reviewed by a GPhC-registered prescriber, and why our supply comes through official LillyDirect channels, directly from Eli Lilly's UK distribution. The pens we send are genuine KwikPens, not repackaged or decanted product.

If you want a more detailed explanation of what sits inside the pen, read our guide to tirzepatide content.

06 · Tirzepatide and its mechanism

How tirzepatide works in the body

Tirzepatide is the first treatment of its kind to activate two natural gut-hormone receptors at once: GIP and GLP-1.¹ These are the receptors your own gut hormones normally use after you eat. The medicine is designed to engage them in a sustained, once-weekly way.

Together these help regulate appetite, slow how quickly the stomach empties, and improve the way the body responds to insulin.¹ In practice, most people feel fuller sooner and less hungry between meals, which supports a reduced-calorie diet.¹ The medicine is not a replacement for eating well and moving more. It makes that effort easier to sustain.

This dual action is what distinguishes Mounjaro from single-action GLP-1 medicines such as semaglutide (Wegovy/Ozempic).¹ Both are licensed treatments; which suits you depends on your health profile, tolerance and prescriber advice. Choosing between them is a prescriber conversation, not a composition quiz.

The question of whether tirzepatide is a hormone often comes up. It is a medicine designed to act on hormone receptors, not a hormone your body makes. Your body produces its own GIP and GLP-1 in the gut. Tirzepatide engages the same receptors as your own gut hormones.

That duration is why the dosing is weekly. Tirzepatide has a half-life of about five days, so after a final dose it takes roughly 4–5 weeks to clear the system — there is no way to speed this up, and nothing needs doing while it clears.¹

None of this means the medicine is gentle on everyone. Mild nausea, altered appetite and tiredness in the first days after each injection are the commonest early effects and usually settle. That is why treatment begins on the lowest strength and rises gradually.

07 · The pen and the dose ladder

The KwikPen, strengths and dose ladder

Mounjaro comes as a pre-filled multi-dose pen (KwikPen) in six strengths: 2.5mg, 5mg, 7.5mg, 10mg, 12.5mg and 15mg.¹ Each KwikPen contains four weekly doses.¹³ You do not draw anything up and you do not measure anything yourself. The pen delivers the dose you set.

Everyone starts Mounjaro on 2.5mg once a week.¹ 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. 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

That is why you should never swap pens by guesswork or try to alter what a pen delivers.

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

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

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 new customer's first order is £40 less and every later order is £25 less.

08 · Injecting and storing the pen

Injecting, storing and travelling with the pen

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.

There is no best time of day. Mounjaro works the same morning or evening. What matters is the same day each week. Many people choose a weekend morning so that early side effects fall on days off. You can change your weekly injection day if needed, as long as at least 3 days (72 hours) have passed since your last dose.

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.

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 at a temperature not above 30°C for up to 30 days after first use — useful for short trips — and must then be thrown away. Do not use a pen that has been above 30°C or has been frozen. Keep the pen cap on to protect it from light.¹

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. Check destination rules for travelling with prescription injectables before you fly.

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 — figures circulating online often come from other countries' labels.¹³

Our deliveries use free next-day tracked delivery in discreet, temperature-controlled packaging. Needles, a sharps bin and injection guidance are included with every order.

09 · Results and body composition

Tirzepatide, results and body composition

The trial evidence for tirzepatide reports changes in total body weight. 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

For someone starting at 100 kg, 20.9% is about 21 kg. That is a worked example of arithmetic, not a prediction for you, and trial averages do not predict your own result.

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. Trials measured results at 72 weeks — think in months, not days, and judge progress by trend, not individual weigh-ins.¹

Early loss includes water weight, so the trend over weeks matters more than any single weigh-in. Some people notice appetite change and early loss in week one, others feel little until a higher dose. Both are normal.

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. If you are curious how real journeys look, our page on Mounjaro transformation discusses what progress can realistically look like.

10 · Natural Mounjaro and counterfeits

"Natural Mounjaro", supplements and counterfeit pens

There is no natural form of Mounjaro. Tirzepatide is a manufactured prescription medicine, and supplements marketed as "natural Mounjaro" or "nature's Ozempic" do not contain it. If you see a list of herbal or vitamin ingredients sold under that label, it is a different product with a different evidence base.

Supplements of this kind are available cheaply without assessment, carry no clinical oversight, and their dosing is not standardised. Dramatic weight-loss claims in their marketing are not supported by the trial evidence that exists for tirzepatide. A product being sold as natural says nothing about whether it is safe or effective for you.

The more serious risk is counterfeit or unregulated tirzepatide. Sellers on social media, marketplaces and messaging apps may offer pens, vials or powders at tempting prices, or offer to supply without a consultation or prescription. Those products have no verified composition. You cannot tell by looking what is in them, how strong they are, or whether they have been stored correctly. The MHRA publishes counterfeit medicine alerts and runs the Yellow Card scheme for reporting problems.⁷

A few checks protect you:

• Buy only from a pharmacy that appears on the GPhC register. Ours is GPhC 9012878, and you can verify our registration directly.¹²
• Be wary of any seller who will supply without a consultation reviewed by a prescriber.
• Expect a genuine branded KwikPen with a leaflet and an expiry date printed on the box.
• Avoid anything labelled "research use", which is not for human use.

Our own supply is official LillyDirect supply, sourced directly from Eli Lilly's UK distribution, and every pen is a genuine KwikPen. If you ever suspect a problem with any medicine, report it through the Yellow Card scheme.¹⁹

The same logic applies to anything described as a "research" version of newer compounds. Medicines in development should not be bought from unregulated sellers.

11 · Safety and what to avoid

Safety, long-term effects and what to avoid

Details of side effects are in the patient leaflet, and you should tell your prescriber about any new or lasting symptom.¹

Read the leaflet from your pack. Tell the prescribing team about all your medical conditions and every other medicine you take, including those bought without a prescription. If you take insulin or sulfonylureas, doses may need adjusting because of the risk of low blood sugar, so your prescriber should know. The same applies when your dose changes.

Most side effects are digestive. The most common, affecting more than 1 in 10 people, are nausea, diarrhoea, vomiting, constipation and abdominal discomfort. They are most likely when starting or moving up a dose and for most people ease within days to a few weeks.¹ Do not alter doses yourself.

Is there anything you must avoid? The leaflet lists what to avoid and when to seek help, and that is the document to follow. Beyond it, general advice is to keep to the weekly schedule, rotate injection sites, store pens properly, and never share a pen. Mounjaro is used alongside a reduced-calorie diet and increased physical activity.

If you notice a new symptom, discuss it with your prescriber rather than searching forums. Report suspected side effects through the MHRA Yellow Card scheme.¹⁹

If you use more Mounjaro than you should, talk to a doctor immediately. If you wonder about fluid effects, read whether Mounjaro is a diuretic.

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 nothing ships automatically.

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

13 · NHS and private access

NHS and private access to Mounjaro

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.

The composition of the medicine is the same whichever route you take. A genuine Mounjaro KwikPen contains tirzepatide whether it comes through an NHS prescription or a regulated online pharmacy. What differs is access, timing and cost to you. On the NHS in England, the prescription charge is £9.90 per item unless you are exempt.

Privately, the consultation with us is free, the price shown is the price paid, and there are no hidden fees. Your answers are reviewed by a GPhC-registered prescriber, not a scoring script. 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 is the same day when ordered by 3pm, with free next-day tracked delivery. Saturday delivery is £14.99.

Planning the cost is sensible. At standard prices a first year costs £2,711.88 if you stay on 5mg after your 2.5mg starting pen, up to £3,599.88 if you step up through every dose to 15mg. A new customer's first order is £40 less and every later order is £25 less. For other maintenance doses the monthly prices are £279.99 at 7.5mg, £290.99 at 10mg and £319.99 at 12.5mg. Prices checked 10 October 2026. Payment is by Visa or Mastercard, Klarna or pay-monthly options, and there are no subscriptions.

Whichever route you choose, the safest approach is the same: a prescriber's assessment, a genuine pen, and a leaflet you have actually read. To start the process, our Mounjaro consultation takes only a short health questionnaire.