Tirzepatide PI: Reading the Patient Information Leaflet Before You Start

Step 1: Before you open the pen, the sections that protect you before a single dose

The PI opens with two sections that most people skip: "What you need to know before you use Mounjaro" and the list of contraindications. These are worth reading first, not last. The contraindications cover situations where tirzepatide must not be used at all, including a personal or family history of medullary thyroid carcinoma or Multiple Endocrine Neoplasia syndrome type 2. If you transferred from another provider or have a more complex medical history, this is the section a prescriber checks before authorising treatment.

Equally important is the interactions section. Tirzepatide slows gastric emptying, which affects how quickly other medicines are absorbed. The PI specifically flags this for oral contraceptives: for the first four weeks of treatment and for four weeks after each dose increase, an additional non-oral method of contraception (such as condoms) is recommended because pill absorption may be reduced. The NHS England guidance on weight-management injections covers this in practical terms and is worth reading alongside the leaflet. If you take HRT orally, the PI directs you to discuss transdermal alternatives with your doctor for the same reason.

This is a question our prescribers hear most weeks: "Does Mounjaro affect my pill?" The answer is in the PI, and it is yes, for the specific windows described above.

Step 2: The injection guide, what the PI shows that a quick search cannot

Section three of the PI is a step-by-step visual injection guide for the KwikPen. Each pen contains four weekly doses. The PI confirms the three approved injection sites (abdomen, thigh and upper arm) and instructs you to rotate the site with each injection to reduce the chance of localised reactions such as redness or firmness under the skin.

Storage instructions are set out here too. The PI specifies refrigeration at 2–8°C as the standard condition; there is a limited window during which the pen can be kept at room temperature, and the exact duration is stated in the leaflet itself. Always refer to your own leaflet for this figure rather than a third-party source, because storage windows are confirmed on the approved labelling, not on general websites. If a pen has been left out for longer than the leaflet allows, contact your prescriber or pharmacist before using it. If you have questions about the injection process, our FAQs address some of the most common practical concerns.

One practical note: used pens and needles must be disposed of in an approved sharps container, which the PI reminds you about at the end of the injection guide. Never place used pens in household recycling.

Step 3: Side effects and when to act, the PI's urgency hierarchy explained

The side effects section in the PI is graded by frequency and by the response required. Common effects (those affecting at least one in ten people) are predominantly gastrointestinal: nausea, diarrhoea, vomiting, constipation and indigestion. These are most likely to appear after starting treatment or after a dose increase, and typically ease within the first couple of weeks as the body adjusts.

The PI also lists effects that are less common but require prompt medical attention. Acute pancreatitis is one of them: severe or persistent stomach pain, particularly pain that radiates through to the back with or without vomiting, is the described warning sign, and the PI is explicit that you should stop treatment and seek urgent help if this occurs. The MHRA reinforced this in a Drug Safety Update for GLP-1 medicines issued in January 2026. Signs of a serious allergic reaction (swelling of the face, lips or throat, difficulty breathing, rapid heartbeat) are also listed as requiring immediate medical help.

Tirzepatide carries a Black Triangle (▼) symbol, which means it is subject to additional monitoring by the MHRA. The PI encourages patients to report any suspected side effects through the Yellow Card scheme, even if they are not sure whether the medicine caused them. You can report online or through the Yellow Card app. For broader context on how tirzepatide works as a licensed weight-management medicine, that page covers the mechanism in more depth.

Step 4: Connecting the PI to your ongoing clinical care

The PI is a reference document, not a substitute for the clinical relationship with your prescriber. It cannot account for your individual health history, other medicines you take, or how your weight-management journey develops over time. For that reason, the PI consistently directs readers back to their doctor or pharmacist rather than encouraging self-management of dose changes or missed injections.

If you are considering private treatment, eligibility for tirzepatide as a weight-management medicine is outlined in the Mounjaro treatment overview. The licensed criteria cover adults with a BMI of 30 or above, or 27 or above alongside at least one weight-related health condition; lower BMI thresholds apply for some ethnic backgrounds under UK guidance. How tirzepatide works in the body is explained in detail on a dedicated page if you want the pharmacology before your consultation.

The PI also notes that tirzepatide is used alongside a reduced-calorie diet and increased physical activity, not instead of them. Weight lost during treatment is better maintained when those habits are embedded, and your prescriber will discuss this as part of ongoing clinical review. At our pharmacy, every repeat order involves a fresh clinical review before the next pen is issued, the leaflet's instructions on what to report between doses give you a ready-made checklist for those conversations.

For context on how private tirzepatide treatment is priced, this page covers the changes to Mounjaro's UK list price and what they mean in practice. If you are still weighing up whether Mounjaro or tirzepatide is the right way to think about your treatment options, that page sets out the relationship between the two clearly. When you feel ready to discuss whether treatment is right for you, checking your eligibility is a good first step, and if you want detail on a specific dose, the tirzepatide 30 page covers what that stage of treatment involves.