Before pricing, before providers, before choosing between semaglutide and tirzepatide, there is a prior question: are you clinically eligible for GLP-1 therapy at all? The criteria are more specific than the marketing suggests, the contraindications are absolute rather than advisory, and the differences between US, UK, and NHS eligibility are substantial. This guide sets out who qualifies, who does not, and what a proper assessment should cover.

Quick Takeaway:

• Standard criteria: BMI of 30 or above, or 27 or above with at least one weight-related condition
• Absolute contraindications include personal or family history of medullary thyroid carcinoma and MEN2 syndrome
• GLP-1s are contraindicated in pregnancy and while breastfeeding
• NHS eligibility criteria in the UK are stricter than private prescribing criteria
• Licensed indications require medication to be used alongside a reduced-calorie diet and increased physical activity

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The Standard BMI Criteria

The licensed indications for Wegovy and Zepbound in adults are broadly consistent:

• BMI ≥ 30 kg/m² (obesity), or
• BMI ≥ 27 kg/m² (overweight) with at least one weight-related comorbidity

Qualifying comorbidities typically include:

• Type 2 diabetes
• Hypertension
• Dyslipidaemia (abnormal cholesterol or triglycerides)
• Obstructive sleep apnoea
• Cardiovascular disease
• Non-alcoholic fatty liver disease
• Osteoarthritis attributable to weight

Both are indicated as an adjunct to a reduced-calorie diet and increased physical activity — a detail routinely omitted from telehealth marketing but written into the approvals themselves.

Where BMI Falls Short

BMI is a population screening tool, not a diagnostic measure of individual health. It does not distinguish fat from muscle, does not account for fat distribution, and performs differently across ethnic groups.

Two practical consequences:

• Lower thresholds for some populations. Many clinical guidelines apply lower BMI thresholds for people of South Asian, Chinese, and some other ethnic backgrounds, where cardiometabolic risk rises at lower BMI values.
• Muscular individuals may be misclassified. A person with high muscle mass may exceed a BMI threshold without carrying excess adipose tissue.

Some providers have begun assessing broader metabolic risk rather than BMI alone — Hims & Hers has publicly described evaluating factors including sleep apnoea and high blood pressure alongside BMI. That is clinically defensible and closer to how obesity medicine specialists actually think.

Absolute Contraindications

These are not risk factors to weigh. They are reasons the medication should not be prescribed:

• Personal or family history of medullary thyroid carcinoma (MTC)
• Multiple Endocrine Neoplasia syndrome type 2 (MEN2)
• Pregnancy, and in most guidance, actively trying to conceive
• Breastfeeding
• Known hypersensitivity to the active ingredient or excipients

Both drug classes carry a boxed warning regarding thyroid C-cell tumours observed in rodent studies. Whether this translates to human risk is not established, but the contraindication is absolute in the labelling.

Important: If you have a family history of thyroid cancer, you must disclose it — even if you are unsure of the type. A questionnaire that asks and a patient who answers honestly is the only safeguard in a telehealth pathway. This is not a box to tick past.

Conditions Requiring Caution

Not contraindications, but circumstances requiring careful clinical judgement:

• History of pancreatitis. GLP-1s have been associated with pancreatitis; prior episodes warrant caution.
• Gallbladder disease or gallstones. Rapid weight loss increases gallstone risk independently, and GLP-1s have been associated with gallbladder events. See our article on GLP-1 agonists and gallstones.
• Diabetic retinopathy. Rapid improvement in glucose control can transiently worsen retinopathy.
• Severe gastrointestinal disease, including gastroparesis.
• Type 1 diabetes. These medicines are not a substitute for insulin.
• History of eating disorders. Appetite-suppressing medication requires careful consideration and monitoring.
• Severe renal or hepatic impairment.
• Concurrent medications — particularly oral medicines with narrow therapeutic windows, since delayed gastric emptying affects absorption.

UK and NHS Eligibility

UK private prescribing broadly follows the same BMI thresholds as elsewhere: 30 and above, or 27 and above with a weight-related condition.

NHS eligibility is considerably stricter and set through NICE guidance and local commissioning. NHS weight management operates in tiers, with Tier 3 specialist multidisciplinary services being where anti-obesity medication is typically considered. Typical Tier 3 criteria involve higher BMI thresholds, documented comorbidities, and prior engagement with lifestyle services — though thresholds vary by area and are lower for some ethnic groups.

NICE has recommended tirzepatide for weight management within defined criteria, with NHS rollout phased and prioritised by clinical need. Some areas commission remote Tier 3 services such as Oviva, delivered free via GP referral.

If you are in the UK, ask your GP two questions before paying privately: am I eligible for Tier 3 weight management, and am I eligible for NHS tirzepatide.

What a Proper Assessment Should Cover

A questionnaire-only pathway with no laboratory work is common in cash-pay telehealth and is not automatically unsafe — but it places the burden of accurate disclosure entirely on you. Providers that include labs, such as LifeMD and Sesame, are doing more thorough medicine.

Frequently Asked Questions

What BMI do I need for a GLP-1 prescription?

The standard licensed criteria are a BMI of 30 or above, or 27 or above with at least one weight-related condition such as type 2 diabetes, hypertension, dyslipidaemia, or obstructive sleep apnoea.

Who cannot take GLP-1 medications?

Absolute contraindications include a personal or family history of medullary thyroid carcinoma, Multiple Endocrine Neoplasia syndrome type 2, pregnancy, breastfeeding, and known hypersensitivity to the medication.

Can I take a GLP-1 if I've had pancreatitis?

A history of pancreatitis requires careful clinical judgement rather than being an absolute bar. GLP-1s have been associated with pancreatitis, so disclose any prior episodes and discuss the risk explicitly with your prescriber.

Are the NHS criteria different from private criteria?

Yes, and considerably stricter. NHS access typically runs through Tier 3 specialist weight management with higher BMI thresholds, documented comorbidities, and prior lifestyle service engagement. NICE has recommended tirzepatide within defined criteria, with phased rollout.

Do I need blood tests before starting?

Many cash-pay telehealth providers do not require them. Baseline testing — HbA1c, lipids, liver and renal function, and thyroid — is better practice, particularly if you have any relevant history. If your provider does not order labs, consider obtaining them independently.

What if I don't meet the BMI criteria?

Anti-obesity medication is not the only option. Lifestyle intervention, structured behavioural programmes, and other prescription options exist. See our alternative treatments guide. Be cautious of any provider willing to prescribe outside licensed criteria without a clear clinical rationale.

Bottom Line

Eligibility is not a formality, and it is not primarily about BMI. The contraindications are absolute, the cautions are real, and the quality of the assessment determines whether problems are caught before they happen.

Disclose everything, including family history you are unsure about. Push for baseline labs if your provider does not order them. And in the UK, check your NHS eligibility before paying privately — the criteria are stricter but the cost difference is enormous.

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Medical disclaimer: Informational only, not medical advice. This guide summarises general eligibility criteria and cannot substitute for individual clinical assessment. GLP-1 receptor agonists are prescription medicines with real risks and contraindications. Consult a qualified healthcare professional.

Sources: FDA prescribing information for Wegovy and Zepbound; NICE obesity management and tirzepatide guidance; European Medicines Agency product information; NHS weight management service information.

Date reviewed: August 2026