What to expect in Mounjaro week 4

Step 1: finishing the 2.5 mg pen, what the first four weeks are actually doing

The 2.5 mg starting dose has one job: settling your system into treatment. It is not the dose at which most weight loss occurs. The titration schedule works this way deliberately, beginning at the lowest strength reduces the likelihood of nausea, vomiting and digestive discomfort hitting hard all at once. If you started with your first Mounjaro injection, you may have noticed little change in the scales for the first couple of weeks, even if your appetite was already shifting.

By week 4 most people have taken four injections and used the full contents of a single pen. What tends to be noticeable by now: reduced hunger between meals, smaller portions feeling more satisfying, and in some cases a reduced interest in foods that previously triggered overeating. These appetite effects are the mechanism at work, tirzepatide activates both the GIP and GLP-1 receptors involved in satiety and gastric emptying. The scales may not reflect that yet. Weight lost in the first month is commonly between 1 and 3 kg, sometimes less, a long way from the averages seen in SURMOUNT-1, but that trial ran for 72 weeks. The trajectory builds.

Side effects, if you had them, typically peak in the first two weeks and then ease. By week 4 on Mounjaro, many people find nausea has largely passed and digestion is settling into a new normal.

Step 2: the week 4 dose review, what a prescriber is looking at

In a properly supervised treatment plan, week 4 is a clinical checkpoint. The standard titration moves from 2.5 mg to 5 mg here, but only if the prescriber is satisfied you have tolerated the starter dose. At nume, every repeat requires a fresh clinical review, a real prescriber reads your update, checks how you have responded and confirms whether stepping up is appropriate. No automated process makes that call.

A few things a prescriber considers: whether GI side effects have resolved sufficiently, whether there are any new symptoms to assess, and your current weight and general wellbeing. If tolerance has been poor, staying on 2.5 mg for another four weeks is a legitimate option rather than pushing the dose up before you are ready. The goal is the highest dose you tolerate well, reached at a pace that keeps side effects manageable. Understanding how long Mounjaro typically takes to produce results helps set sensible expectations at this stage.

This is also a good moment to review lifestyle factors alongside treatment. Protein intake, hydration and staying active all support what the medicine is doing, your prescriber or a dietitian is the right person to advise on specifics.

Step 3: what if there has been no weight loss by week 4?

This is one of the questions our prescribers hear most often, and it is worth addressing plainly. Seeing little change on the scales after four weeks at 2.5 mg is common and does not mean treatment is failing. The opening dose is sub-therapeutic for most people, it is an adjustment phase, not a productive weight-loss phase in its own right.

The bigger concern would be little or no weight loss after several months at the maintenance dose. That is a different situation and one covered separately on the page specifically about no weight loss at week 4. For now, if appetite has shifted at all (if portions feel smaller, if hunger between meals is quieter) the medicine is doing something. The weight often follows once the dose steps up.

Factors that can slow progress at any point: alcohol, calorie-dense liquids, disrupted sleep, high stress levels. None of these are reasons to stop treatment; they are things to work on alongside it. For context on what full-course results look like, the NICE appraisal of tirzepatide (TA1026) summarises the clinical evidence across the SURMOUNT trial programme.

Step 4: what to expect when the 5 mg pen arrives

Once the prescriber confirms the step-up, the 5 mg pen is dispensed. At nume, if you order before midday on a working day, the pen is dispatched that day after clinical approval and arrives the next working day via DPD. It comes in plain, unbranded packaging, tracked, so you know exactly when it is landing. The 5 mg pen looks identical to the 2.5 mg version in terms of how you use it; the device is the same KwikPen format.

The move to 5 mg is where many people begin to see more tangible changes in weight, though the GI side effects may reappear briefly as your body adjusts to the higher dose, the same pattern as the very beginning, often milder and shorter. Injection-site rotation continues as before: abdomen, thigh or upper arm, moved each week. Storage in the fridge remains standard.

Mounjaro is a long-term treatment for most people. If you are thinking about the bigger picture (how long the treatment runs, what comes after, or what it costs across the titration schedule) those are all things our prescribers work through with patients. The guidance on treatment duration is a useful read before that conversation.

If you are considering starting or have questions about eligibility, check your eligibility with our prescribers, consultation is free.