What to do before starting Mounjaro: a practical preparation guide

What the trial data tells us about early treatment, and why preparation matters

The SURMOUNT-1 trial, published in the New England Journal of Medicine, followed more than 2,500 adults with obesity over 72 weeks and found average body-weight reductions of around 20–21% at the 15mg maintenance dose. What the headline figures don't advertise is that almost every participant started at 2.5mg, a dose whose job is tolerability, not treatment. The titration schedule exists because tirzepatide slows gastric emptying and alters appetite signalling in ways the body needs time to accommodate.

That context matters practically. People who go into the first pen expecting rapid results and no side effects are the ones most likely to be caught off guard. Understanding what the first weeks on Mounjaro actually look like changes that. The preparation steps below aren't optional extras; they map directly onto what clinical guidance and the prescribing information flag as the things most likely to affect early tolerability and safety.

NHS guidance on tirzepatide is clear that Mounjaro should be used alongside a reduced-calorie diet and increased physical activity. Setting those habits in motion before the first injection (rather than trying to change everything at once) is sensible, and supported by the trial's own design, which included lifestyle support for all participants.

Medicines, supplements and the contraception conversation your prescriber needs to have

The single most overlooked preparation step is compiling a complete list of every medicine, supplement and herbal remedy you take. This isn't bureaucracy. Because tirzepatide slows gastric emptying, it can affect how quickly other medicines are absorbed, and for oral contraceptives the implications are specific enough that the MHRA and NHS England have issued explicit guidance on it.

Women taking the combined pill or progestogen-only pill should discuss contraception with their prescriber before starting. The MHRA advises using a non-oral contraceptive method (such as condoms) for the first four weeks of tirzepatide treatment and for four weeks after each dose increase, because pill absorption may be reduced during that window. There is no equivalent evidence of this effect with semaglutide, so this is tirzepatide-specific.

NHS England also advises people on oral HRT to discuss switching to a transdermal format (patch or gel) for the same absorption reason. If you take medicines for blood pressure, thyroid conditions or anything where timing and absorption matter, flag them. A prescriber reviewing your case at nume (a real clinician, not an automated system) will work through your medicines list as part of the assessment. Bring everything, including things bought over the counter.

Eating, hydration and storage: the practical logistics

The evidence on GI side effects is consistent across the tirzepatide trials: nausea, loose stools and reflux are most likely in the 24–48 hours after an injection, particularly at the start of a new dose. A few practical changes in the days before your first pen can reduce the severity. The tips most commonly cited in clinical guidance are straightforward: eat smaller portions at each meal, cut heavily fatty or spiced food, stay well hydrated, and avoid lying flat shortly after eating. If you are wondering whether taking Mounjaro before bed might help you manage any side effects, that timing question is covered in detail on the linked page.

Protein intake deserves a mention. Tirzepatide reduces appetite, and if overall food intake drops sharply without attention to protein, muscle loss becomes a real risk. Thinking about protein-rich foods you genuinely like (eggs, fish, Greek yoghurt, pulses) before you start means you're not figuring that out when you're already nauseous.

Storage is the logistical piece people most often forget. Mounjaro pens are refrigerated at 2–8°C. Check you have adequate fridge space; the pen cannot sit next to something that freezes. Once out of the fridge, the exact room-temperature window is specified in the Patient Information Leaflet, read it before your pen arrives, not on injection day. If you have a scheduled operation or procedure coming up, tell both your surgical team and the prescribing clinician before starting, as NHS England advises informing the anaesthetist that you take a GLP-1 medicine.

Getting the consultation right, what to have ready

The prescription assessment at a regulated service like nume is where your individual circumstances get evaluated. Having certain things to hand makes it thorough rather than perfunctory. Your current weight and height let the prescriber confirm eligibility (BMI ≥30, or ≥27 alongside a weight-related health condition). Any existing diagnoses (type 2 diabetes, hypertension, high cholesterol, sleep apnoea) are relevant both to eligibility and to monitoring. A note of any recent blood tests, particularly kidney function or lipid results, is useful context.

If you've been on Mounjaro before through another provider and want to transfer, bring evidence of your current dose; nume's clinical policy requires this before prescribing at a dose above the starter. The cost of treatment is a reasonable thing to think about in advance too, you can see what's included in nume's pricing on the treatment page, where consultation, clinical review, delivery and aftercare are covered under one figure rather than itemised separately. If you want a clearer sense of the kind of results people have experienced, the Mounjaro before and after page brings together real-world outcomes alongside the trial data.

One practical note: nume dispatches same-day for orders placed before 12pm on weekdays, once a prescriber has reviewed and approved the consultation. If your mornings are tight, knowing that cut-off before you start means your first delivery lands when you're expecting it. When you're ready, check your eligibility and start your free consultation, a GPhC-registered prescriber will review your answers the same day.