Mounjaro Yellow Card: How to Report a Side Effect (October 2026)

01 · The scheme

What the Yellow Card scheme is, and should you use it?

The Yellow Card scheme is the UK system for reporting suspected side effects of medicines, run by the MHRA. Its purpose is to spot safety problems early, so that the regulator can update warnings and product information where needed.¹⁹ Reports from people actually taking a medicine are a central part of that picture.

You should consider a report if you have had a symptom you think may be linked to Mounjaro, whether it is mild or serious. You do not need to be certain. The scheme exists precisely because a single clinician or patient rarely sees the whole pattern.

Reporting is not a substitute for medical care. Your first step with a new or worsening symptom is to speak to the prescriber who looks after your treatment. If you are with us, our prescribing team offers side-effect support as part of ongoing monthly reviews. For anything severe or sudden, such as severe, persistent stomach pain, swelling of the face or throat or difficulty breathing, get medical help straight away rather than filing a form first.

02 · Step by step

How to report Mounjaro on Yellow Card

You can file a Yellow Card report in a few minutes using the Yellow Card website or the Yellow Card app, available on the main phone app stores.¹⁹ The process is the same whether you are a patient, a carer or a healthcare professional, although the form asks slightly different questions.

• Choose your route: the website on a computer or phone, or the app if you want to save details as you go.
• Say who you are reporting as: a patient or member of the public, or a healthcare professional.
• Name the medicine: select Mounjaro or tirzepatide, and add the strength of the KwikPen you were using, from 2.5mg to 15mg.
• Describe the reaction: what happened, when it started relative to your doses, and how it affected you.
• Add other medicines and conditions: including contraception, diabetes treatments and anything you bought without a prescription. If you take the contraceptive pill, Mounjaro can reduce how well it is absorbed: switch to a non-oral method, or add a barrier method such as condoms, for 4 weeks after starting Mounjaro and for 4 weeks after each dose increase.
• Submit: keep any confirmation or reference you are given.

If you are not sure which medicine caused a reaction, you can still report. List everything you take, and the MHRA can look at the pattern across many reports.

03 · What to include

What to include in a Mounjaro report

A useful report is specific. The more precise your details, the more the MHRA can do with them, and a vague report is much harder to interpret.¹⁹

• The product name, strength and, if you have it, the batch number printed on the pen carton or label.
• The date you started Mounjaro and the dates of any dose changes.
• The date the symptom began, how long it lasted and whether it has settled.
• What you did about it: whether you paused, saw a clinician, or needed treatment.
• Your other medicines, supplements and relevant health conditions.

Keep the carton and pen until you have reported, especially if you suspect the product itself. The patient information leaflet lists the side effects that are already recognised, and it is worth reading alongside your report so you can tell your prescriber what is and is not expected.¹³

Do not include other people's personal details. Your own contact details are optional in some cases, but giving them lets the MHRA follow up if they need more information.

04 · What reports can tell you

What Yellow Card reports can and cannot tell you

Yellow Card data are safety signals, not statistics on how common a problem is. A report records a suspicion. It does not prove the medicine caused the event, and it says nothing about how many people took the medicine without any trouble.¹⁹

Counts of reports rise when a medicine is widely used, when it is in the news, and when people are encouraged to report. They are not a measure of risk.

The same applies to questions such as how many people have had pancreatitis from Mounjaro. A number of reports cannot answer that, because nobody knows from the reports alone how many people took the medicine or how many events would have happened anyway. Your prescriber is the right person to ask about what is known about a risk.

05 · Symptoms to raise

New symptoms: what to do besides reporting

Tell your prescriber about any new symptom while you are on Mounjaro, then consider a Yellow Card report. The most common side effects, affecting more than 1 in 10 people, are nausea, diarrhoea, vomiting, constipation and abdominal discomfort, and they are most likely when starting treatment or moving up a dose.

Some symptoms people ask us about are not listed side effects at all. Where something is not in the product information, the honest answer is that it is not listed as a side effect in the UK patient leaflet. That does not mean you should ignore it. Mention it to your prescriber and, if you suspect a link, report it so it can be assessed.¹⁹

Questions we see often include digestive changes and stool or urine colour. Our guides on yellow diarrhoea on Mounjaro, yellow stools and bright yellow urine explain what to watch for and when to speak to someone.

If you stop, tirzepatide has a half-life of about five days, so after a final dose it takes roughly four to five weeks to clear the system. There is no way to speed this up, and nothing needs doing while it clears.¹

06 · Counterfeit pens

Reporting suspected fake Mounjaro

Yellow Card is also the route for reporting a suspected counterfeit or falsified medicine, not only side effects. The MHRA publishes alerts about falsified Mounjaro pens, and the scheme asks you to report a product you doubt.⁷

Warning signs include a seller offering to supply without a consultation or prescription, a pen that looks different from the one you were prescribed, damaged or unsealed packaging, or a supplier you cannot check. Mounjaro is a prescription-only medicine, supplied only after an online consultation reviewed by a GPhC-registered prescriber.¹

You can check any UK pharmacy on the GPhC register. EverydayMeds is registered under GPhC 9012878, and we supply genuine KwikPens through official LillyDirect supply direct from Eli Lilly's UK distribution. If you have already used a pen you now doubt, speak to a healthcare professional, keep the packaging, and report it.

07 · The "Mounjaro card"

"Mounjaro card": Yellow Card or something else?

A Yellow Card is a reporting scheme, not a card you carry or a discount you receive.

• Yellow Card: the MHRA scheme for reporting suspected side effects. Nothing is issued to you and there is no cost.
• Discount cards: our guide to the Mounjaro discount card explains how savings really work.

Similarly, a "yellow injection for weight loss" is a description of appearance or colour rather than a product name; our page on the yellow injection for weight loss explains the confusion. If a seller gives you a name you cannot match to a licensed product, check it on the GPhC register before buying.¹²

08 · Treatment context

Why safety reporting sits alongside treatment

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. It comes as a pre-filled multi-dose pen (KwikPen) in six strengths: 2.5mg, 5mg, 7.5mg, 10mg, 12.5mg and 15mg.¹

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 Whether you are treated through the NHS or privately, the Yellow Card scheme works the same way.

09 · Our aftercare

Side-effect support with EverydayMeds

If you are one of our customers, you do not have to work this out alone. Ongoing monthly reviews, dose-titration and follow-up assessments are carried out by our prescribing team, and side-effect support is part of that aftercare. Repeat orders re-check suitability, and nothing is shipped automatically.

You can reach support 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. Needles, sharps bin and injection guidance are included with every order.

Tell us what happened, then decide with your prescriber whether to continue, pause or change dose. If you also file a Yellow Card report, you are helping the regulator as well as yourself. Our free companion app, GLPTrackr, lets you log doses and symptoms, which makes it easier to give accurate dates later.

10 · 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