Mounjaro and the Yellow Card scheme: reporting side effects the right way

Step 1: Decide whether you need urgent medical help first

Before you open Yellow Card, the most important question is whether your symptoms need attention right now. The Yellow Card scheme is a reporting tool, not a helpline. Certain symptoms during Mounjaro treatment call for same-day medical contact: severe, persistent stomach pain that radiates toward your back (a possible sign of acute pancreatitis, highlighted in the MHRA's January 2026 Drug Safety Update for GLP-1 medicines), signs of a serious allergic reaction, or symptoms of dehydration after prolonged vomiting or diarrhoea. If any of those apply, ring 111 or 999 as the situation demands, and report to Yellow Card once you are stable.

For side effects that are uncomfortable but not an emergency (persistent nausea, constipation, injection-site irritation, fatigue, headache) Yellow Card is exactly the right next step. These are the reports that build the safety picture regulators rely on, and Mounjaro's monitoring status means every report during this period carries particular weight. A question our prescribers hear regularly: do you have to wait until the side effect has fully resolved to report? You do not. Reports submitted while a side effect is ongoing are just as valid.

Step 2: Go to the Yellow Card website and complete the form

Visit yellowcard.mhra.gov.uk, this is the only official MHRA portal for reporting. You can report as a patient or carer without any professional login. The form asks for the medicine name (Mounjaro, and the dose if you know it), the suspected side effect in your own words, when it started, how long it lasted, what happened next, and some basic information about you (age range, sex, other medicines). You do not need to produce the pen from the fridge or the Patient Information Leaflet, though having either to hand makes the dose and batch number easier to find.

Most people complete it in under ten minutes. If you are new to tirzepatide and want to understand the medicine itself more fully, our guide to tirzepatide covers the clinical background. The MHRA may follow up if they need clarification, though most reports are processed without contact. You will receive a reference number by email, which is worth keeping.

Step 3: Tell your prescriber, and keep reporting to them too

Yellow Card and your prescriber serve different purposes. The MHRA is collecting population-level signal; your prescriber is managing your individual treatment. Both matter. Let your prescriber or the clinical team supporting your prescription know about any side effect, especially if it is affecting your ability to continue at the current dose. At nume, our aftercare team is available seven days a week for exactly this kind of conversation, a side effect is not a reason to simply stop injecting without guidance, because abrupt discontinuation sometimes has its own implications worth discussing.

If you are taking Mounjaro privately and want to review how it fits your situation, you can also check whether your experience matches what others have reported by looking at published Yellow Card data for Mounjaro. The MHRA publishes aggregated reports publicly, and the pattern of what is commonly reported versus what is rare is genuinely useful context.

Step 4: Know what else Yellow Card covers

Yellow Card is not only for side effects from legitimate treatment. It is also the right place to report a suspect medicine, for example, if you have reason to believe a Mounjaro pen was counterfeit or was supplied without a valid prescription from an unverified seller. The MHRA takes these reports seriously; significant enforcement action has followed patient tip-offs. If you are at all uncertain whether your supply came through a legitimate, GPhC-registered pharmacy, Yellow Card's suspect-medicines section is the place to raise it.

There are some common questions that drift toward Yellow Card searches but are really about different things. Changes in urine colour during treatment, for instance, are more often down to hydration than the medicine itself, this page looks at that specifically. And if you are thinking about the cost of ongoing treatment and want to understand what a transparent private price actually includes, our guide on Mounjaro costs in the UK is a sensible place to start. Some patients also enjoy lighter corners of the Mounjaro community, and if you are looking for something to celebrate a milestone, we have put together a Mounjaro birthday card that makes a thoughtful gift for someone marking a treatment anniversary. For anything about beginning treatment through nume, the right move is to speak to our prescribers.