How the Mounjaro programme works — and what to expect from it

What does the Mounjaro programme actually involve week to week?

Think of the programme less as a diet plan and more as a medically supervised structure. Your prescriber starts you on 2.5 mg, a dose chosen because it gives your digestive system time to adapt, not because it is where the therapeutic weight-loss effect is strongest. Most people stay there for four weeks, then move to 5 mg, then 7.5 mg, and so on, with the prescriber reviewing your progress and tolerance before each step up.

The injection itself is once weekly, delivered via a pre-filled KwikPen into the abdomen, thigh or upper arm, rotating the site each time. The pen contains four doses, so one pen lasts a month. You can read the full dosing schedule, storage requirements and injection guidance in the NHS tirzepatide patient information, which is the clearest plain-English summary available.

Between injections, the programme asks something of you too. Tirzepatide slows gastric emptying and dials down appetite signals, but the medicine works best when you meet it halfway, adequate protein, plenty of water, and some form of movement you can actually sustain. None of that requires perfection. It requires consistency. Some people researching their options come across Mounjaro being sold through Telegram channels, and it is worth knowing that sourcing prescription medicine this way carries real risks around authenticity, storage and clinical oversight. A question the prescribers at our clinical team hear regularly is whether you have to follow a strict diet plan: the honest answer is no formal plan is mandated, but eating habits matter a great deal for how much of the weight you keep off.

Who qualifies for the Mounjaro programme under UK licensing?

The licensed criteria for tirzepatide in the UK are set out in the medicine's Summary of Product Characteristics. Adults with a BMI of 30 or above are eligible, as are those with a BMI of 27 or above if they have at least one weight-related health condition, prediabetes, type 2 diabetes, high blood pressure, high cholesterol or obstructive sleep apnoea are typical examples. BMI thresholds are adjusted downward by 2.5 kg/m² for people from South Asian, Chinese, Middle Eastern, Black African or African-Caribbean backgrounds, in line with UK clinical guidance.

That said, a number on a BMI chart is only the starting point. A prescriber also considers your full medical history: other medicines you take, conditions that might rule out tirzepatide (a personal or family history of certain thyroid cancers or pancreatitis, for instance), and whether the timing makes sense for your circumstances. Pregnancy, breastfeeding and trying to conceive are situations where tirzepatide is not recommended. The medicine is not licensed for anyone under 18.

If you use oral contraception, there is a practical interaction worth knowing about: the MHRA advises adding a non-oral contraceptive method for the first four weeks of treatment and for four weeks after each dose increase, because the pill's absorption can be affected. There is a detailed page on tirzepatide and the progesterone-only pill if that is relevant to you, and a broader look at progesterone and Mounjaro for those on other hormonal methods.

What side effects come with the programme, and when do they matter most?

The most commonly reported effects are gastrointestinal: nausea, loose stools, constipation, indigestion and burping. They tend to be most noticeable in the first week or two after starting, or after a dose increase, and settle for most people as the body adjusts. Fatigue, headache and dizziness are also reported, particularly early on.

A few symptoms warrant prompt medical attention. Severe stomach pain that spreads toward the back (especially if persistent and accompanied by vomiting) should be assessed urgently, as this can indicate pancreatitis, a known but uncommon complication of GLP-1 class medicines. The MHRA highlighted this risk in a January 2026 Drug Safety Update. Signs of a serious allergic reaction or symptoms of gallbladder problems (pain in the upper right abdomen, fever, yellowing of the skin) are also reasons to seek help promptly. You can report any suspected side effect through the MHRA Yellow Card scheme.

Most people find the programme manageable, particularly when dose increases are paced carefully. Slowing the titration, eating smaller meals, and staying well hydrated are practical steps that help, though the right approach for your situation is a conversation for your prescriber, not a general guide.

How does the private Mounjaro programme differ from the NHS route?

The NHS is rolling out tirzepatide in phases. As of mid-2026, access is limited to those with a BMI of 40 or above plus four or more of five qualifying conditions, with further cohorts due to open from around March 2027. The full NICE eligibility criteria are summarised in NICE technology appraisal TA1026. Even for those who qualify, waiting lists through specialist services can be long, and GP prescribing under the new 2026 contract is optional, so availability varies by practice.

A private prescription route through a regulated online pharmacy means no referral, no waiting list and no requirement to meet the phased NHS thresholds, subject to the prescriber's clinical assessment. If you are curious about what that looks like in practice, our guide to getting Mounjaro through a UK pharmacy walks through the steps. For a broader view of weight-loss treatment options beyond tirzepatide, the weight-loss treatment overview covers the landscape.

One thing worth understanding before comparing services: the price you see quoted online does not always reflect the full cost of the programme. A legitimate programme includes clinical assessment, a prescription from a registered prescriber, the medicine itself, and ongoing aftercare. What that combination costs (and what to make of prices across providers) is covered in more detail on our Mounjaro information page. The short version is that for a prescription medicine, the cheapest option answers the wrong question.