The UK's most complete GLP-1 guide
Every Question Answered. Every Side Effect Explained.
- How GLP-1 medications work
- Mounjaro vs Wegovy compared
- Injection instructions
- Side effects & solutions
- What to eat on treatment
- FAQs answered
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Best Fat Loss Medication in the UK
If you're looking for prescription medication to support weight management, the UK has several licensed options available. Prescription fat loss medications work alongside healthy lifestyle changes and are only prescribed following a clinical assessment by a GP or licensed prescriber. Understanding what's available, how these medications work, and whether you're eligible is essential before starting any treatment. This UK health guide explains the evidence-based options, NHS guidance, and how to access them safely.
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Calculate Your BMI Instantly
Enter your height and weight below. Supports both imperial (stone & lbs) and metric (kg). Results include NHS category, healthy weight range, and ethnicity adjustments.
What Is BMI and Why Does It Matter?
Body Mass Index (BMI) is the most widely used screening tool for assessing whether your weight falls within a healthy range. Used by the NHS, GPs, and weight management services across the UK, BMI provides a quick snapshot of your weight relative to your height. The formula is simple: your weight in kilograms divided by your height in metres squared (kg/m²).
While BMI isn't a perfect measure — it doesn't account for muscle mass, bone density, or fat distribution — it remains the standard first step in identifying potential weight-related health risks including type 2 diabetes, cardiovascular disease, high blood pressure, and certain cancers.
The NHS also recommends adjusted thresholds for people of South Asian, Chinese, or Black African heritage — a BMI of 23 or above is classified as overweight, and 27.5 as obese. Our calculator includes this adjustment as a one-click toggle.
UK-Approved Fat Loss Medications and How They Work
The main prescription-only fat loss medications licensed in the UK are Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). Mounjaro and Wegovy are once-weekly injections; Saxenda is a daily injection. All three work as GLP-1 receptor agonists or dual GIP/GLP-1 agonists — they mimic natural hormones that regulate appetite and blood sugar.
- Mounjaro: A dual GIP and GLP-1 agonist. Clinical trials showed average weight loss of 15–21% of body weight. Doses range from 2.5 mg to 15 mg weekly.
- Wegovy: A GLP-1 agonist with average weight loss around 15% of body weight in trials. Maximum dose is 2.4 mg weekly.
- Saxenda: A daily GLP-1 injection. Typically results in around 5–clinically studied weight loss in clinical studies.
Individual results vary significantly, and all medications are most effective when combined with reduced-calorie diet and increased physical activity. A licensed prescriber assesses suitability for each person.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
How It Works
Three simple steps to understand your weight and take action.
Enter your height and weight in our free calculator. Get your BMI, NHS category, healthy weight range, and ethnicity-adjusted thresholds instantly.
If your BMI suggests you're overweight or obese, explore our GLP-1 calculators to project potential weight loss on Mounjaro or Wegovy.
Use our progress tracker to log your weight weekly, visualise your journey with charts, and stay motivated — all stored privately in your browser.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
NHS Guidance and UK Eligibility Criteria
You may be eligible for prescription fat loss treatment if you have a BMI of 30 or above, or a BMI of 27–29.9 with at least one weight-related health condition such as type 2 diabetes, high blood pressure, or sleep apnoea. For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, lower thresholds apply — eligibility may begin at BMI 27.5 or above due to higher health risks at lower BMI levels.
On the NHS, access is through specialist tier 3 weight management services, typically requiring a GP referral. Availability varies significantly by region. Private prescribing is also available following an online clinical assessment. Either way, a prescriber must assess your individual circumstances before issuing a prescription.
Check your personal BMI using our free BMI calculator above — this will help you understand whether you might meet initial eligibility thresholds. Alongside medication, sustainable weight management requires dietary changes, increased physical activity, and behavioural support. The NHS Weight Loss Plan and local weight management services can provide guidance on lifestyle changes. If you're considering fat loss medication, discuss options with your GP, who can assess your health, medications, and suitability. Our GLP-1 weight loss calculator can also help you understand potential outcomes at different medication doses.
- Dual GIP/GLP-1 receptor agonist
- Up to 22.5% body weight loss (SURMOUNT-1)
- Weekly injection, dose escalation over 20+ weeks
- Available via private prescription in the UK
- Doses: 2.5mg → 5mg → 7.5mg → 10mg → 12.5mg → 15mg
- GLP-1 receptor agonist
- Up to 15–17% body weight loss (STEP trials)
- Weekly injection, 5-step dose escalation
- NHS & private prescription available
- Doses: 0.25mg → 0.5mg → 1mg → 1.7mg → 2.4mg
Mounjaro vs Wegovy: Head-to-Head
A side-by-side comparison of the two most popular GLP-1 weight loss medications available in the UK.
| Feature | Mounjaro | Wegovy |
|---|---|---|
| Drug class | Dual GIP/GLP-1 agonist | GLP-1 agonist |
| Active ingredient | Tirzepatide | Semaglutide |
| Avg. weight loss | 15–22.5% | 12–17% |
| Key trial | SURMOUNT-1 (2022) | STEP 1 (2021) |
| Max dose | 15 mg weekly | 2.4 mg weekly |
| Escalation period | 20–32 weeks | 16–20 weeks |
| Administration | Weekly injection (pen) | Weekly injection (pen) |
| NHS availability | Private prescription only | NHS & private |
| Approx. private cost | £150–£250/month | £150–£300/month |
| Common side effects | Nausea, diarrhoea, constipation | Nausea, vomiting, diarrhoea |
Data sourced from SURMOUNT-1 and STEP 1 clinical trials. Costs are approximate and vary by provider. Always consult a prescriber.
Am I Eligible for Weight Loss Medication?
In the UK, eligibility for GLP-1 weight loss medications like Mounjaro and Wegovy is based on your BMI and overall health profile.
- BMI of 30 or above (obese)
- Age 18 or over
- No contraindicated conditions
- Committed to lifestyle changes
- BMI of 27 or above
- Plus type 2 diabetes
- Or high blood pressure
- Or obstructive sleep apnoea
Use our BMI calculator to check whether your BMI falls within the eligible range.
How We Built These Tools
Every calculator and guide on myweightcheck is built with accuracy and transparency in mind. Our BMI calculator uses the standard WHO formula with NHS-aligned category thresholds. Our GLP-1 projections are modelled on published clinical trial data from SURMOUNT and STEP studies.
All data stays on your device. We don't require sign-ups, and we don't store your health information on any server. Your progress tracker saves data locally in your browser using localStorage, so only you can see it.
We're based in the UK and our tools are designed specifically for UK users — supporting stone & lbs by default, referencing NHS guidelines, using NICE-approved medication data, and linking to GPhC-registered pharmacies.
Frequently Asked Questions
Common questions about BMI, weight loss medications, and our free UK tools.
What is the best fat loss medication in the UK?
There is no single "best" medication — the most suitable depends on your health, BMI, preferences, and clinical assessment. Mounjaro and Wegovy are the most commonly prescribed; both are once-weekly injections with strong clinical trial evidence. Your GP or prescriber will assess which is appropriate for you.
How much weight can you lose on fat loss medication?
Clinical trials show average weight loss of 5–21% of body weight depending on the medication and dose. Individual results vary significantly based on genetics, lifestyle adherence, diet, and exercise. Weight loss is not assured, and results are best when medication is combined with dietary changes and physical activity.
Can I get fat loss medication on the NHS in the UK?
Yes, but access is through specialist tier 3 weight management services, usually via GP referral. Availability varies by region and waiting times can be long. Private prescribing is available without NHS referral through GPhC-registered online pharmacies following a clinical assessment.
Are fat loss injections safe in the UK?
Prescription fat loss medications are licensed and monitored by the MHRA. Common side effects include nausea, diarrhoea, and constipation. Serious side effects are rare but can include pancreatitis and gallbladder issues. Always discuss risks and benefits with your prescriber before starting treatment.
How do I know if I'm eligible for fat loss medication?
Use our free BMI calculator to check your BMI. General eligibility is BMI 30+ or BMI 27–29.9 with weight-related health conditions. Lower thresholds apply for certain ethnic backgrounds. A prescriber will conduct a full clinical assessment to confirm suitability and check for contraindications.
Ready to take control of your weight loss journey?
Start with a free BMI check, explore your GLP-1 options, or begin tracking your progress today. No sign-up. No cost. Just results.