In the UK, prescription weight-loss treatment is generally available privately to adults with a BMI of 30 or above, or 27 and above with a weight-related health condition such as type 2 diabetes, high blood pressure or sleep apnoea. Lower BMI thresholds apply for people from some ethnic backgrounds, and NHS access uses stricter criteria. Meeting a number isn't the whole story, though — a clinical assessment decides suitability, not the calculator alone.
The BMI thresholds explained
Licensing for medicines like Mounjaro (tirzepatide) and Wegovy (semaglutide) sets the baseline most UK providers work from:
- BMI 30+ ("obese" range) — eligible for assessment on BMI alone
- BMI 27–30 ("overweight" range) — eligible with at least one weight-related condition, such as type 2 diabetes or prediabetes, high blood pressure, high cholesterol, obstructive sleep apnoea, cardiovascular disease or PCOS
NICE recommends adjusted (lower) thresholds for people of South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean family background, because health risks begin at lower BMIs in these groups — in practice thresholds are reduced by 2.5 kg/m².
BMI is a blunt tool — it can't tell muscle from fat — which is one reason a human prescriber reviews every application rather than a calculator approving it.
What the assessment actually checks
A legitimate UK provider will assess more than height and weight:
- Medical history — certain conditions rule these medicines out (for example a personal or family history of medullary thyroid cancer or MEN2, or a history of pancreatitis), and others need extra care
- Current medicines — interactions and combined effects, particularly with diabetes medication
- Pregnancy and fertility plans — these medicines must not be used during pregnancy or while breastfeeding, and should be stopped in advance of trying to conceive
- Eating disorder history — appetite-suppressing medicines need careful clinical judgement here
- Previous weight-loss medication — what you've taken and how you responded shapes the plan (and dose) you're offered
- Identity and weight verification — reputable providers verify who you are and your stated weight, often with photo or video evidence. If a website will sell you a weight-loss injection with no checks at all, that's a red flag, not a convenience
Why honest answers matter more than "passing"
The assessment isn't an exam to beat. Understating your weight or hiding history can lead to a medicine that's unsafe for you, a wrong starting dose, or serious complications. Prescribers decline applications when treatment isn't appropriate — a decline protects you, and a good provider will explain alternatives rather than just saying no.
Private vs NHS access
The criteria above cover private treatment. The NHS prescribes weight-loss medicines under significantly stricter criteria — currently prioritising people with the highest BMIs and multiple weight-related conditions, with access rolling out in phases through GP services and specialist weight-management clinics. If you might qualify via the NHS, that route is worth understanding first: see our guide to NHS weight-loss medication eligibility in 2026. Many people who don't meet NHS thresholds do meet private ones — that gap is exactly who regulated private services exist for.
What happens after you qualify
Approval means starting at the lowest dose of your prescribed medicine and titrating up gradually under prescriber review — regardless of how much weight you want to lose. Expect check-ins around dose changes, weight tracking, and an expectation of engagement with eating and activity changes. Treatment is a programme, not a product.
Frequently asked questions
What BMI do I need for Mounjaro or Wegovy in the UK?
Privately: generally BMI 30+, or 27+ with a weight-related health condition, with lower thresholds for some ethnic backgrounds. NHS criteria are stricter and phased.
Can I get weight loss injections if I'm just a few kilos overweight?
No — below the licensed thresholds these medicines aren't appropriate, and a responsible prescriber will decline. The risks aren't justified for small amounts of weight.
Why was my application declined?
Common reasons: BMI below threshold, a contraindicated condition or medicine, pregnancy or conception plans, or safety concerns in your history. A decline is a clinical safety decision — you're entitled to an explanation and alternatives.
Do I need to see someone in person?
Not necessarily — online assessment is legitimate when it's thorough and prescriber-led. Expect identity and weight verification; be wary of any service that skips them.
References
- NICE. Overweight and obesity management (NG246 / relevant technology appraisals for semaglutide and tirzepatide).
- Wegovy — Summary of Product Characteristics. medicines.org.uk.
- Mounjaro KwikPen — Summary of Product Characteristics. medicines.org.uk.
- NHS England. Interim commissioning guidance: tirzepatide for weight management.
- General Pharmaceutical Council. Guidance for registered pharmacies providing pharmacy services at a distance.