Body Mass Index (BMI) is one of the primary criteria used to determine whether you are eligible for Mounjaro in the UK. While it is a useful screening tool, it has well-known limitations that are worth understanding.
How to Calculate Your BMI
BMI is calculated by dividing your weight in kilograms by your height in metres squared:
BMI = weight (kg) ÷ height (m)²
For example, if you weigh 95 kg and are 1.70 m tall: 95 ÷ (1.70 × 1.70) = 95 ÷ 2.89 = 32.9.
You can also use the free NHS BMI calculator at nhs.uk for a quick result.
BMI Categories
- Under 18.5: Underweight
- 18.5–24.9: Healthy weight
- 25–29.9: Overweight
- 30–34.9: Obese (Class I)
- 35–39.9: Obese (Class II)
- 40+: Obese (Class III)
Mounjaro Eligibility Thresholds
In the UK, Mounjaro is typically prescribed for adults with:
- A BMI of 30 or above, or
- A BMI of 27 or above with at least one weight-related comorbidity (such as type 2 diabetes, hypertension, obstructive sleep apnoea or cardiovascular disease).
Some online pharmacies may have slightly different eligibility criteria, so always check the specific requirements during the consultation process.
Limitations of BMI
BMI does not distinguish between muscle mass and fat mass. This means:
- Very muscular individuals may have a high BMI but low body fat.
- Older adults with low muscle mass may have a “normal” BMI but carry excess fat.
- BMI does not account for fat distribution. Central (abdominal) fat carries higher health risk than fat stored on hips and thighs.
For these reasons, many clinicians also consider waist circumference. A waist measurement above 94 cm for men or 80 cm for women indicates increased metabolic risk, regardless of BMI.
Adjusted BMI for Ethnic Minorities
NICE guidance recognises that South Asian, Chinese, African-Caribbean and other Black ethnic groups may experience obesity-related health risks at lower BMI thresholds. Prescribers may use adjusted cut-offs (e.g., BMI 23 instead of 25 for overweight, and 27.5 instead of 30 for obese) for these populations.
What If You Are Just Below the Threshold?
If your BMI is slightly below 30 but you have documented comorbidities, discuss this with your prescriber. They may still consider you eligible based on your overall clinical picture. MedsLens can help you find UK pharmacies with clear eligibility criteria and transparent consultation processes.