GLP-1 Eligibility UK: What BMI Do You Need for Wegovy or Mounjaro?

BMI is not a perfect measure of health. Most clinicians will tell you that. Yet it remains the primary gating criterion for GLP-1 medications in the UK, for both NHS and private prescribers. Understanding where you sit relative to the thresholds, and what flexibility exists within those thresholds, is the practical starting point for anyone considering semaglutide or tirzepatide.

The short version: NHS access requires a higher BMI than private access, and having a weight-related health condition can lower the qualifying threshold in both settings. The full picture has more nuance.

The NHS Thresholds

The NHS prescribes Wegovy (semaglutide 2.4mg) through specialist weight management services, not through GPs directly. Access follows criteria set by NICE technology appraisals, which means eligibility is specific.

NICE TA875 criteria for Wegovy on the NHS:

• BMI of 35 or above plus at least one weight-related comorbidity, OR
• BMI of 30–34.9 if referred through a specialist Tier 3 weight management service
• Prescription through a specialist service only (GPs do not prescribe Wegovy independently)

The weight-related comorbidities that qualify include type 2 diabetes, hypertension, obstructive sleep apnoea, non-alcoholic fatty liver disease, dyslipidaemia, and cardiovascular disease.

Important context: NHS access is not simply a matter of meeting the BMI criteria. Demand far exceeds supply. Waiting lists for specialist weight management services vary significantly by region, and some areas have lists stretching to 12 months or longer. Meeting the eligibility criteria on paper does not guarantee timely access.

The Adjusted Threshold for Certain Ethnic Groups

NICE guidance recognises that the health risks associated with obesity manifest at lower BMI values in people of South Asian, Chinese, Middle Eastern, Black African, and African-Caribbean family background.

For these groups, the BMI thresholds are reduced by 2.5 points:

• 32.5 or above with a comorbidity (rather than 35)
• 27.5 or above through Tier 3 (rather than 30)

This adjustment reflects the clinical evidence that adipose tissue distribution and metabolic risk differ by ethnicity in ways that BMI alone does not capture. If you are from one of these ethnic groups, the standard thresholds on most eligibility calculators will not accurately reflect your NHS qualifying status.

Private Prescriber Thresholds

Private prescribers in the UK operate outside NHS formulary restrictions. They are still bound by professional and regulatory standards. A prescriber cannot legally prescribe a medication they do not consider clinically appropriate, but they have more latitude in applying clinical judgement.

Typical private eligibility for Wegovy (semaglutide 2.4mg) or Mounjaro (tirzepatide):

• BMI of 30 or above, OR
• BMI of 27 or above with a weight-related health condition

This lower threshold (30 rather than 35) is why private access is significantly broader than NHS access. Someone with a BMI of 31 and hypertension who cannot access the NHS pathway can usually access treatment privately within weeks.

Weight-Related Conditions That Count

Both NHS and private eligibility can hinge on whether you have a qualifying comorbidity. The following conditions are consistently recognised:

Metabolic:

• Type 2 diabetes or pre-diabetes (HbA1c 42 mmol/mol or above)
• Dyslipidaemia (elevated LDL, triglycerides, or low HDL)
• Non-alcoholic fatty liver disease (NAFLD/MASLD)
• Metabolic syndrome

Cardiovascular:

• Hypertension (BP consistently above 140/90 mmHg)
• Established cardiovascular disease (prior MI, stroke, peripheral arterial disease)
• High 10-year cardiovascular risk score (QRISK3 10% or above)

Respiratory:

• Obstructive sleep apnoea
• Obesity hypoventilation syndrome

Musculoskeletal:

• Osteoarthritis with significant functional impact attributable to weight

Psychological:

• Some private prescribers include obesity-related depression, eating disorder history, or significant quality of life impairment (this varies considerably by provider)

How BMI Is Calculated

BMI = weight in kilograms divided by height in metres squared (kg/m²).

The standard categories in the UK:

• Below 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 or above: Obese Class III (formerly "morbidly obese")

Prescribers use the lower ethnic adjustment thresholds where applicable. If you are calculating your own BMI, use your weight in kilograms and height in metres: divide weight by height squared.

Wegovy vs Mounjaro: Do the Thresholds Differ?

Both medications have similar eligibility thresholds in the UK private market. Mounjaro (tirzepatide) received NICE approval through TA1026 in 2025 with criteria closely mirroring Wegovy's TA875: BMI 35 or above with comorbidity, or BMI 30 via specialist pathway.

In practice, private prescribers apply similar thresholds for both. The clinical decision between them is usually based on patient history, glycaemic status, tolerability, and cost rather than eligibility differences.

Tirzepatide achieves meaningfully greater average weight loss: 20.9% of body weight in SURMOUNT-1 versus 14.9% for semaglutide 2.4mg in STEP 1. Some patients start on semaglutide for cost reasons and switch if response is insufficient.

What If Your BMI Is Just Below the Threshold?

BMI is a snapshot. It will fluctuate with hydration, time of day, and measurement precision. If you are within a few points of a threshold:

Get weighed properly. Use a calibrated scale, first thing in the morning, without shoes, after using the bathroom. Some people find they are closer to qualifying than they realised.

Assess comorbidities. If you have untreated hypertension or elevated fasting glucose that has not been formally investigated, get a blood test. Pre-diabetes or dyslipidaemia may already be present and not yet diagnosed.

Consider ethnicity adjustments. If your ethnic background qualifies for the lower threshold, a BMI of 28 with hypertension may place you within eligibility on some private pathways.

Speak to a prescriber anyway. Many private prescribers use clinical judgement for borderline cases. A patient with BMI 28, severe sleep apnoea, and significant psychological burden from weight may be treated on clinical grounds even if they technically sit below the headline threshold.

NHS vs Private: Which Route Makes Sense?

For the NHS eligibility process in detail, see /guides/nhs-glp1-eligibility-uk. For choosing a private provider once you know you qualify, see /guides/best-glp1-prescriber-uk-2026.

The BMI Limitation Debate

BMI is a population-level statistical measure, not a clinical diagnostic tool. Two people with the same BMI can have radically different body fat percentages, fat distribution patterns, and metabolic profiles.

Waist circumference is a better predictor of visceral fat accumulation and associated metabolic risk. A waist circumference above 88cm in women or 102cm in men (or 80cm/94cm for the lower ethnic thresholds) indicates elevated cardiometabolic risk regardless of BMI.

Some private prescribers incorporate waist circumference, DEXA scan results, or metabolic markers into their eligibility assessment rather than relying on BMI alone. This reflects a more clinically accurate picture but is not universal.

The practical reality is that BMI remains the primary access criterion because it is simple, standardised, and cheap to measure. Until clinical guidelines shift to incorporate broader metabolic phenotyping, BMI is the number you need to know.

Getting a Private Prescription Once You Qualify

If you meet the private eligibility criteria, the process is straightforward:

1. Book a consultation with a CQC-regulated UK prescriber (online or in person)
2. Complete a medical history questionnaire and BMI verification
3. The prescriber reviews and, if appropriate, issues a private prescription
4. Medication is dispensed by a partnered or independent pharmacy

Costs vary by provider. Wegovy typically runs £150–200 per month; Mounjaro £140–180 per month at standard doses. Generic injectable semaglutide is available at lower cost through some providers.

For a breakdown of private prescription costs and providers compared, see /guides/glp1-private-prescription-guide-uk.