What your BMI should be for Mounjaro — and why it's only part of the picture

The biggest misconception: a BMI of 30 means automatic approval

A lot of people arrive at an online consultation having calculated their BMI, hit the threshold, and assumed approval is a formality. That isn't how it works, and a clinic that implied otherwise would be cutting corners. Mounjaro is a prescription-only medicine (tirzepatide, made by Eli Lilly) and UK law requires a prescriber to make an individual clinical judgement before issuing any prescription. The BMI threshold in the licence exists to define the population the medicine was tested in and approved for, not to serve as a pass/fail gate that replaces clinical thinking.

So yes, a BMI below 30 (or below 27 with a relevant condition) would make Mounjaro outside its licensed indication, and a responsible prescriber won't issue it. But meeting the BMI number opens the door; it doesn't walk you through it. Your prescriber also looks at your medical history, current medicines, any contraindications, and whether treatment is appropriate for your specific situation. That review is what protects you. You can read more about the consultation process on our Mounjaro treatment page.

The actual thresholds, including the 27 BMI route and ethnic-background adjustments

Mounjaro's UK licence covers two groups. First: adults with a BMI of 30 or above, regardless of whether they have other conditions. Second: adults with a BMI of 27 to 29.9 who also have at least one weight-related condition, the most common qualifying conditions are type 2 diabetes, pre-diabetes, hypertension, high cholesterol, obstructive sleep apnoea and osteoarthritis. If you sit in the 27–29.9 range, your prescriber will want to confirm which condition applies and may ask for evidence of a diagnosis.

There is also an important adjustment for some ethnic backgrounds. NICE's appraisal of tirzepatide, NICE TA1026, notes that BMI thresholds should sit 2.5 kg/m² lower for people of South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean backgrounds, reflecting evidence that health risks from excess weight occur at lower BMI values in these populations. In practice that means a threshold of 27.5 (instead of 30) or 24.5 (instead of 27 with a condition). If this applies to you, mention it during your consultation.

The NHS BMI calculator is a quick way to get your number before you start. Bear in mind BMI doesn't account for muscle mass, body composition or fat distribution, your prescriber knows this too, and it's one reason the clinical review matters beyond the number itself.

NHS eligibility versus private treatment: different criteria, different routes

If you've been reading about Mounjaro on the NHS, you may have noticed the eligibility bar is considerably higher than the private licence thresholds above. NICE TA1026 sets out a phased NHS rollout: as of summer 2026, the NHS is prescribing tirzepatide to adults with a BMI of 40 or above who have four or more qualifying conditions (high blood pressure, dyslipidaemia, obstructive sleep apnoea, cardiovascular disease or type 2 diabetes). A second cohort (BMI 35 to 39.9 with four or more conditions) opened in June 2026. Waiting lists at GP practices vary, and not every practice has opted into the new prescribing arrangements yet.

Private treatment works differently. The relevant threshold is the medicine's licensed indication, not the NHS commissioning criteria. That means a BMI of 30 (or 27 with a qualifying condition) is the baseline, and a prescriber assesses suitability from there. There is no referral, no waiting list, and no requirement to have four comorbidities. For people who want to understand what your BMI needs to be for Mounjaro on a private basis compared with the NHS route, our guide to the BMI you need for Mounjaro sets out how the two routes compare in more detail, and our overview of what your BMI has to be to get Mounjaro covers the qualifying criteria in plain terms.

Cost is naturally a consideration. Private Mounjaro treatment is priced per month and varies by dose and provider; our Mounjaro price page covers what the market looks like and what one transparent price actually includes. Worth knowing before you compare figures across providers.

What happens if your BMI changes during treatment?

Mounjaro works. For many people, BMI falls meaningfully over the course of treatment, that's the point. What it doesn't mean is that a lower BMI during treatment suddenly makes you ineligible to continue. Prescribers make repeat assessments based on the clinical picture at each review, not a snapshot BMI taken partway through. If you started at a BMI of 31 and have lost weight, your prescriber considers progress, tolerability, ongoing benefit and your health overall.

At nume, every repeat order goes through a fresh clinical review by a GPhC-registered prescriber, not an automatic renewal, a real re-assessment. That review is where your progress is weighed against the plan going forward. Questions about timing and scheduling are also common at this stage, and if you've ever wondered whether you can take Mounjaro a day earlier than planned, our page on that covers what the guidance says. If you have questions about how that works in practice, our FAQs cover the repeat process, or you can get in touch directly. Our clinical team, including our lead prescriber Mostafa Damghani, is available seven days a week for aftercare queries.

If you're ready to find out whether you're clinically suitable, starting a free consultation is the straightforward next step, no commitment, no upfront payment, just a clinical review by a named prescriber who will give you a clear answer.