To be considered for Mounjaro (tirzepatide) through a UK private weight-loss service, you usually need a body mass index (BMI) of 30 or above, or a BMI of 27–30 if you also have a weight-related health condition such as type 2 diabetes, high blood pressure or sleep apnoea. You must also be 18 or over, and treatment is only prescribed after a clinical consultation confirms it is safe and appropriate for you.
This article explains how BMI is calculated, why these thresholds exist, how private and NHS routes differ, and what else a prescriber checks before Mounjaro can be prescribed.
The BMI thresholds for Mounjaro at a glance
- BMI 30 or above — this falls into the obesity range and generally meets the criterion on its own.
- BMI 27 to under 30 — this may qualify if you also have at least one weight-related condition (for example type 2 diabetes, high blood pressure, or obstructive sleep apnoea).
- Aged 18 or over — Mounjaro is not licensed for under-18s for weight management.
These criteria are consistent across the licensed weight-loss injections and tablets. You can see them alongside each treatment on our treatments overview.
How to work out your BMI
BMI is a simple screening measure that compares your weight to your height. To calculate it, divide your weight in kilograms by your height in metres squared (kg/m²).
For example, someone who is 1.70m tall and weighs 90kg has a BMI of 90 ÷ (1.70 × 1.70) = 31.1. That would fall into the obesity range.
You don't need to do the maths yourself — our free online consultation captures your height and weight and works out your BMI for you as part of checking eligibility. You can begin that at start your free consultation.
How BMI ranges are grouped
| BMI (kg/m²) | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Healthy weight |
| 25 – 29.9 | Overweight |
| 30 and above | Obesity |
Why the 27–30 range needs a weight-related condition
Below a BMI of 30, the potential benefits of a prescription weight-loss medicine are weighed more carefully against the risks. The presence of a weight-related condition tips that balance, because losing weight can meaningfully improve those conditions.
Weight-related conditions that may bring the lower threshold into play include type 2 diabetes, high blood pressure, and obstructive sleep apnoea, among others. A prescriber will assess your full health picture rather than looking at a single number.
Does ethnicity change the threshold?
For some people from South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean backgrounds, health risks linked to weight can occur at a lower BMI. A prescriber may take this into account when assessing your individual eligibility, so it is important to answer the consultation honestly and fully.
Private eligibility vs the NHS route
The BMI-based criteria above reflect eligibility through a regulated private service. Access to Mounjaro on the NHS is different and generally more restricted, with additional criteria, specialist referral pathways and waiting lists that vary by area.
If you are exploring the NHS route, speak to your GP about local availability. Choosing a private route does not remove the need for a proper clinical assessment — at The Weight Clinic every treatment is still prescribed only where clinically appropriate.
BMI is the start, not the whole picture
Meeting the BMI threshold does not automatically mean Mounjaro will be prescribed. A GPhC-registered prescriber also checks whether it is safe for you.
Mounjaro may not be suitable if you:
- are pregnant, planning pregnancy or breastfeeding;
- have type 1 diabetes;
- have a personal or family history of medullary thyroid carcinoma or MEN2;
- have a history of pancreatitis or severe gastrointestinal disease;
- have an active eating disorder;
- have severe liver or kidney impairment;
- have a known allergy to tirzepatide.
This is why the consultation matters: it protects you, and it is a legal requirement because Mounjaro is a prescription-only medicine.
What Mounjaro is and how it works
Mounjaro contains tirzepatide and is unusual in activating two gut-hormone receptors — GLP-1 and GIP — at the same time. This helps reduce appetite and supports weight loss alongside changes to diet and activity.
It is a once-weekly self-injection, started at a low 2.5mg dose and increased gradually (5, 7.5, 10, 12.5mg) up to a maximum licensed dose of 15mg. Titrating slowly helps your body adjust and can reduce side effects.
In the SURMOUNT-1 trial, participants on the 15mg dose lost on average 22.5% of body weight over 72 weeks, alongside lifestyle support. Individual results vary; not everyone reaches this. You can read more on the Mounjaro treatment page.
Common side effects
The most common side effects (affecting more than 1 in 10 people) are nausea, diarrhoea, constipation, vomiting, decreased appetite and fatigue. Rare but serious risks include severe allergic reactions, acute pancreatitis, severe hypoglycaemia, severe gastrointestinal disease and worsening diabetic retinopathy.
If you experience a side effect, you can report it through the MHRA Yellow Card scheme at https://yellowcard.mhra.gov.uk/.
If your BMI doesn't quite meet the threshold
If your BMI is below the criteria, a prescription weight-loss medicine may not be appropriate right now. A conversation with your GP or a registered pharmacist can help you understand other supportive options.
If you do meet the criteria, other licensed options include the Wegovy injection and the once-daily Wegovy Tablet. You can compare the injectable options on our weight-loss injections page.
How to check whether you're eligible
The simplest way to find out is our free online consultation. It works out your BMI, asks about your health, and a registered prescriber reviews your answers to decide whether treatment is clinically appropriate.
- Complete the free online consultation about your health and weight.
- A GPhC-registered prescriber reviews your answers.
- A short video consultation takes place where clinically needed.
- If suitable, your medicine is dispensed by our UK pharmacy and sent by tracked delivery, with ongoing prescriber support.
The consultation is free and you only pay if a treatment is prescribed and you choose to go ahead. Mounjaro prices start from £160 per month depending on the dose. Learn more about The Weight Clinic or check your eligibility now. A prescription is never guaranteed — it is issued only if clinically appropriate.
This article is for information only and is not a substitute for personalised medical advice. Weight-loss medicines are prescription-only, are not suitable for everyone, and are prescribed only after a clinical consultation with a GPhC-registered prescriber. Individual results vary. Always speak to a UK-registered pharmacist or doctor before starting or changing any prescription medication.
