What to do when you're on Mounjaro: a practical guide

What the evidence says about diet and activity on tirzepatide

The SURMOUNT-1 trial (which randomised 2,539 adults with obesity over 72 weeks) tested tirzepatide alongside a reduced-calorie diet and increased physical activity programme, not instead of one. Participants at the 15mg dose achieved an average body-weight reduction of around 20–21%, a result that reflects the combination rather than the drug alone. Tirzepatide's dual GIP and GLP-1 receptor activity slows gastric emptying and reduces appetite, which makes it considerably easier to eat less, but the food choices you make inside that reduced appetite still shape your results.

In practical terms, this means prioritising protein at each meal. When appetite falls sharply, it is easy to under-eat protein without noticing, and that can lead to muscle loss rather than fat loss. Aim for a source of protein at breakfast, lunch and dinner (eggs, fish, poultry, legumes, Greek yoghurt) and treat it as the anchor of the plate rather than an afterthought. The day-to-day habits worth building on Mounjaro extend well beyond the injection itself.

Physical activity compounds the benefit. Strength-based exercise in particular helps preserve lean mass during rapid weight loss. You do not need a gym membership; resistance bands, bodyweight circuits or carrying groceries count. The NHS advises adults to aim for at least 150 minutes of moderate activity per week alongside any weight-management programme, and that guidance applies here too. Start gently if you are new to exercise, the medicine may reduce your energy in the early titration weeks.

Injection technique, site rotation and storage

Getting the injection right matters more than many people expect. Tirzepatide is administered subcutaneously (into the fatty layer just beneath the skin) using the pre-filled KwikPen. The three licensed sites are the abdomen (at least 5cm from the navel), the front of the thigh, and the outer upper arm. Rotating between sites each week prevents lipohypertrophy, a hardening of the tissue that reduces absorption and can blunt the medicine's effect.

Inject on the same day each week, at roughly the same time. Consistency keeps the drug level steady. If you miss a dose by fewer than four days, take it as soon as you remember and then resume your usual day. If more than four days have passed, skip that dose entirely and continue from your next scheduled injection. For anything more complicated (a missed dose that falls around a dose increase, for instance) guidance on timing and scheduling is worth reading, and your prescriber can advise on your specific situation.

Storage: keep the pen refrigerated at 2–8°C until you are ready to use it. There is a limited window during which it can be kept at room temperature, but that window varies and the Patient Information Leaflet is the definitive source, check it rather than relying on any general figure. Never freeze the pen, and keep it away from direct light. Inspect the solution before each injection; it should be clear and colourless.

Managing side effects, especially in the first few weeks

Nausea, loose stools, constipation, indigestion and fatigue are the side effects people encounter most often when on Mounjaro, particularly after starting or after a dose increase. For most people they settle within one to two weeks as the body adjusts. Eating smaller portions, avoiding rich or very fatty meals, and eating slowly all reduce the likelihood of nausea. Staying well hydrated is important regardless, vomiting or diarrhoea can lead to dehydration quickly, and dehydration in turn strains the kidneys.

If you experience severe, persistent stomach pain that radiates towards the back, seek medical attention promptly. The MHRA issued a Drug Safety Update in January 2026 highlighting acute pancreatitis as an infrequent but serious risk with GLP-1 medicines, and that symptom pattern warrants urgent assessment. You can report any suspected side effect via the MHRA Yellow Card scheme, which helps regulators monitor real-world safety data.

It is worth acknowledging that arriving at this point (starting treatment, getting to grips with injection days and side-effect windows) can feel more complicated than expected. That is normal. Our prescribers hear this regularly. The adjustment period is temporary, and it does pass.

Monitoring your progress and when to flag something to your prescriber

Weighing yourself weekly, at the same time of day, on the same scales, gives a more reliable picture than daily weigh-ins. Weight fluctuates with hydration, food volume and hormonal cycles, so a single day's number can mislead. The NHS recommends recording progress over weeks rather than days for exactly this reason.

NICE's appraisal of tirzepatide (TA1026) notes that if weight loss is less than 5% after six months at the highest tolerated dose, the clinical case for continuing is reviewed. That is a clinical conversation, not an automatic stop, context matters, and what to do if Mounjaro seems to have stopped working covers this in more detail. Equally, the decision about when to stop treatment is one your prescriber should be part of, not something to make unilaterally.

At nume, every repeat order goes back to a real clinician before it is dispensed. A prescriber reads your updated information and checks that continuing is still the right call. You can find more about what to avoid on Mounjaro and the full Mounjaro overview if you want a broader picture. For questions about cost as treatment continues, the Mounjaro price guide sets out what to expect. And if at any point something doesn't feel right, our team is available seven days a week.