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

01 · The short answer

What are the components of Mounjaro?

Mounjaro has one active component, tirzepatide, and a group of inactive components called excipients. The active ingredient produces the medical effect. The excipients keep the liquid stable, comfortable to inject and safe to store. That split applies to almost every injectable medicine, and Mounjaro is no exception.

Mounjaro is the brand name for tirzepatide, a once-weekly injectable prescription medicine made by Eli Lilly. In the UK it is licensed for weight management in adults and for type 2 diabetes.¹

Formulations can be updated, and the leaflet inside your box is the legal source. The patient information leaflet and the SmPC are published on the electronic medicines compendium.¹¹³

02 · What to decide

Do the components matter for you?

For most readers the components matter in two ways. The first is allergy: if you have ever reacted to a medicine or an ingredient in one, you should read the leaflet before you start and tell the prescriber. The second is understanding what you are injecting, so that nothing in the pen surprises you.

If you are weighing up whether the medicine suits you at all, the components are only a small part of the picture. Eligibility, other medicines you take, your health history and your goals all feed into the decision. The prescriber who reviews your consultation looks at those together.

Mounjaro 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.

When you are ready to look at treatment, the Mounjaro pen with prices and consultation is the place to start. The 2.5mg starter pen has a standard price of £169.99, and new customers save £40 on their first order with code FIRST40. An automatic £25 reorder discount applies to every future order (code DOSE25). All six doses are in stock, and the consultation itself is free. For broader context, see our weight loss clinic overview.

03 · At a glance

Active and inactive components compared

The leaflet supplied with your pen always takes priority over any website, including ours.

Related guides: Mounjaro contraindicaciones and Her mounjaro.

04 · Active ingredient: tirzepatide

The active ingredient: tirzepatide

Tirzepatide is the only active ingredient in Mounjaro. Every strength of the pen contains it; what changes between strengths is the amount, not the substance.

Mounjaro is the brand name for tirzepatide, a once-weekly injectable prescription medicine made by Eli Lilly. In the UK it is licensed for weight management in adults and for type 2 diabetes.¹ The brand name belongs to Eli Lilly, while tirzepatide is the generic name you will see in clinical papers, NICE guidance and the BNF.⁴¹¹

People often ask whether Mounjaro contains anything else with a pharmacological effect, such as a second drug, a stimulant or a hidden additive. The product information lists tirzepatide as the active substance and nothing else. The effects you feel come from that one molecule acting on two receptor systems.

It also helps to understand what tirzepatide is not. It is not a supplement, a herbal extract or a vitamin. It is a regulated prescription medicine that has been through clinical trials and licensing in the UK. That matters because online sellers sometimes use the word "tirzepatide" loosely on products that are not the licensed pen. Genuine Mounjaro comes as a branded KwikPen from an authorised supply chain, which is why we source ours through official LillyDirect supply direct from Eli Lilly's UK distribution.

If you want to read the formal description, the SmPC on the electronic medicines compendium sets out the composition, the strengths and the licensed uses in the regulator's own words. The BNF entry gives dosing and safety information in a format used by UK clinicians.¹¹ Both are free to read, and reading them is a sensible habit with any medicine you are about to start.

One practical point: because the pen only ever contains tirzepatide as its active substance, you do not need to worry about "extra" compounds being added at higher strengths. Higher strengths simply carry more of the same molecule, which is why your prescriber moves you up gradually rather than all at once.

05 · Inactive ingredients explained

Inactive ingredients (excipients)

The inactive ingredients in Mounjaro are excipients, substances added so the active ingredient can be delivered safely and reliably. They are not intended to have a medical effect. The full, current list is in section six of the patient information leaflet and in the SmPC, so that is where you should confirm it for your own pen.¹¹³

Formulations differ between countries and device types, and a list written for another market may not match the UK KwikPen.

• They keep the liquid at a suitable acidity so the active ingredient stays stable.
• They help the solution match the body's own fluids, which makes injection more comfortable.
• They keep the product sterile and usable across the in-use period of the pen.

For anyone with a known sensitivity to an additive, the leaflet is the document to consult. Read the ingredients section, compare it with anything you have reacted to in the past, and raise it in your consultation. A GPhC-registered prescriber reviews every consultation, and the free online questionnaire gives you a straightforward place to mention allergies.

If you cannot find an answer in the leaflet, our pharmacy support team can help 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. They can point you to the right section of the product information, although questions about clinical suitability go to the prescribing team.

Finally, remember that "inactive" means inactive in terms of the treatment effect. It does not mean risk-free for everyone. Allergic reactions to excipients are possible with many medicines, which is why the leaflet lists them clearly and why reading it before your first injection is worthwhile.

06 · The KwikPen device

The KwikPen: what you actually hold

The Mounjaro KwikPen is a pre-filled, multi-dose pen that delivers the weekly dose through a fine needle. It comes as a pre-filled multi-dose pen (KwikPen) in six strengths: 2.5mg, 5mg, 7.5mg, 10mg, 12.5mg and 15mg.¹ You do not draw anything up or mix anything. The pen is ready to use once you attach a needle and follow the instructions in the box.

Your order contains the pen, the leaflet and instructions for use. Needles, a sharps bin and injection guidance are included with every order from us, so you have what you need to inject safely and dispose of needles properly.

Some readers ask whether Mounjaro comes as a cartridge or a vial. In the UK the product is the KwikPen, and our page on the cartridge versus KwikPen question covers the terminology in more detail. If you see vials or loose "refills" advertised, treat the listing with caution and check whether the seller is a registered pharmacy. You can verify ours on the GPhC register under registration number 9012878.¹²

Storage is part of the pen's practical make-up. Store unopened pens in the fridge, at 2–8°C, until first use; they keep until the printed expiry date. Once you start a pen, it can be kept out of the fridge at a temperature not above 30°C for up to 30 days after first use, and must then be thrown away.¹¹³ For anything beyond that, such as an unopened pen left out of the fridge by accident, follow the patient information leaflet and ask the pharmacy rather than guessing. Our guide to storing your pen covers travel and everyday handling.

The pen is cold-chain shipped. We use free next-day tracked delivery with temperature-controlled, discreet packaging, and same-day dispatch applies when you order by 3pm. When it arrives, put it in the fridge unless you are about to use it, and check the label matches the strength you were prescribed.

Do not share pens, even if you think the needle has been changed. A pen is dispensed for one person against one prescription. The leaflet explains correct needle use and disposal, and reading the instructions for use before your first injection takes only a few minutes.

07 · How tirzepatide works

How the active component works

Tirzepatide works by acting on two natural gut-hormone receptors at the same time. Tirzepatide is the first treatment of its kind to activate 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

In practice, most people feel fuller sooner and less hungry between meals, which supports a reduced-calorie diet. That is the point of the medicine: it makes it easier to follow the diet and activity plan that does the real work of weight management, rather than replacing it.

This dual action is what distinguishes Mounjaro from single-action GLP-1 medicines such as semaglutide (Wegovy/Ozempic). Semaglutide belongs to the class of GLP-1 receptor agonists, meaning it acts on one of the two receptor systems that tirzepatide targets. Neither is better in every circumstance; they are different licensed medicines with different profiles, and the right choice depends on the person.

A few consequences follow from the mechanism:

• Slower stomach emptying is part of why appetite changes. It is also why the prescriber asks about other oral medicines you take.
• Improved insulin response is why the medicine is licensed for type 2 diabetes as well as weight management.
• The effect builds with dose, so treatment starts low and steps up under supervision.

Clearance is the other half of how the component behaves. 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 That slow clearance is why a once-weekly schedule works, and why effects do not vanish the day after a missed or final injection.

If you are comparing medicines, avoid reading trial numbers from different studies side by side as if they were a head-to-head contest. A direct comparison needs a trial that compared the two medicines directly, and your prescriber can explain which evidence applies to your situation.

08 · Allergies and suitability

Allergies, suitability and the components

The components matter most to people who have had a reaction to a medicine before, so tell the prescriber about any allergy during your consultation. The leaflet lists who should not use Mounjaro, including anyone allergic to tirzepatide or to any of the other ingredients listed in it.¹³ Reading that section is a simple safeguard.

Suitability goes well beyond ingredients. A prescriber considers your health history, the medicines you take and your reasons for treatment.

Our process is built around that review. You complete a short, free health questionnaire with no obligation. A GPhC-registered prescriber reviews it, and this is a clinical review, 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. If you are approved, the pharmacy dispenses and dispatches your pen.

There are also practical situations where the components and the way the medicine acts on the stomach become relevant, such as planned procedures. If you are due an operation or sedation, our page on Mounjaro and anaesthesia explains why you should tell the clinical team in advance. Never stop or change a prescribed medicine on your own because of something you read online; speak to the prescriber first.

What if you suspect an ingredient is not agreeing with you? If you develop signs of an allergic reaction, such as swelling of the face or throat or difficulty breathing, get medical help straight away. New symptoms of any kind are worth raising with your prescriber, because they can judge whether the pen, the dose or something unrelated is responsible.

Ongoing aftercare is part of treatment. Monthly reviews, dose-titration and follow-up assessments are carried out by the prescribing team, with side-effect support if you need it. Repeat orders re-check suitability, and there is no auto-shipping, so you remain in control of each order.

09 · Side effects and safety reporting

Side effects, long-term questions and reporting

The possible side effects of tirzepatide are listed in the patient information leaflet and the SmPC, grouped by how commonly they occur.¹¹³

Many people ask about long-term effects, whether any effects are irreversible, how to reduce the risk of pancreatitis, and whether the medicine is hard on the liver. There is no proven way to prevent pancreatitis or gallbladder problems while taking Mounjaro. Before you start, tell your prescriber if you have ever had pancreatitis, gallstones or gallbladder disease, or severe problems with your digestion. Read the relevant sections of the leaflet, and bring your questions to the monthly review.

What you can do in practice:

• Read the leaflet's side-effect section before the first injection, not after.
• Tell the prescriber about any history of pancreas, liver or digestive problems when you complete the consultation.
• Tell your prescriber about any new or lasting symptom instead of waiting for the next review; for severe, persistent stomach pain, get medical help straight away.
• Use the Yellow Card scheme to report suspected side effects to the MHRA.¹⁹

If you notice a symptom that is not on the leaflet's list, tell your prescriber about any new or lasting symptom.

The Yellow Card scheme is run by the MHRA, and anyone can use it, including patients. Reports help regulators spot patterns across the whole population of people taking a medicine. It takes only a few minutes and does not replace telling your prescriber.

Regulators have looked specifically at whether GLP-1 medicines are linked to low mood or suicidal thoughts: the EMA's safety committee reviewed the evidence and concluded in 2024 that it does not support a causal link, and the MHRA keeps this under continuous review.¹⁷ That said, any big change in weight, appetite and routine can affect how you feel; tell your prescriber about any history of depression, and seek help promptly if your mood drops or you have distressing thoughts during treatment.

If you have thoughts of harming yourself or ending your life, get help straight away. Call 999 or go to A&E if you are in immediate danger. In England you can call NHS 111 and choose the mental health option, any time. You can also call Samaritans free on 116 123, day or night. Tell your prescriber about any change in your mood while taking Mounjaro.

10 · What the trials show

What the active ingredient achieved in trials

Evidence for tirzepatide's effect on weight comes from the SURMOUNT-1 trial. 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, and no clinician can promise one. What they do show is that the medicine produced larger average changes than lifestyle measures alone in the people studied.

The same trial reported how many participants reached particular thresholds. At 72 weeks, 85% of participants on 5mg, 89% on 10mg and 91% on 15mg had lost at least 5% of their body weight.² Half of participants on 10mg and 57% on 15mg lost at least 20% of their body weight.²

A worked example helps show scale without implying a promise. For someone starting at 100 kg, 20.9% is about 21 kg. That is straight arithmetic from the trial's average at the top dose, not a forecast for any individual, and it says nothing about how quickly any person would get there.

It is worth being clear about what the trial tells you about components. The results belong to tirzepatide as the active ingredient at the stated doses, taken with diet and activity changes. They do not apply to supplements that borrow the name or to products sold as "natural" alternatives, which have not been tested in this way.

Finally, do not set these numbers beside results from other medicines' trials as though they came from one contest. Different trials recruit different people and measure over different periods. If you want to know how Mounjaro compares with another treatment, ask your prescriber which direct evidence is relevant.

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, private supply and genuine pens

NHS access, private supply and getting a genuine pen

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, the pen should contain the same active ingredient, made by Eli Lilly. The NHS page on tirzepatide is a good neutral reference for how the medicine is used.⁵ The difference between routes is access and cost, not the molecule.

Genuine supply is where components become a safety issue. Counterfeit and unregulated products circulate online, and the MHRA publishes counterfeit medicine alerts and runs the Yellow Card scheme.⁷ Warning signs include a seller offering to supply without a consultation or prescription, loose vials or unbranded products, and dramatic weight-loss claims. Any of these should make you stop.

Check that the seller is a registered pharmacy. EverydayMeds is GPhC-registered, number 9012878, and you can confirm that on the public register.¹² Our Mounjaro is supplied through official LillyDirect supply, direct from Eli Lilly's UK distribution, as genuine KwikPens.

Ordering with us follows three steps. First, complete the free online consultation, reviewed by a GPhC-registered prescriber. Second, payment is taken when you place the order; if the prescriber decides the treatment is not suitable, the order is refunded automatically in full. Third, the pharmacy dispenses and dispatches your pen with free next-day tracked delivery; Saturday delivery is £14.99. You can pay by Visa or Mastercard, Klarna or pay-monthly options, and there are no subscriptions.

If you want to compare prices or start a consultation, the Mounjaro pen page with live prices shows the current figures, checked 12 October 2026. The price shown is the price paid, and the consultation carries no charge.