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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Semaglutide For Weight Loss In The UK
Semaglutide is a once-weekly weight loss injection licensed in the UK under the brand name Wegovy. As a GLP-1 receptor agonist, it may help reduce appetite and support feeling fuller after smaller meals. Access through the NHS is possible via specialist tier 3 services, though private prescribing is also available. Individual results vary, and semaglutide works best alongside reduced-calorie diet and increased physical activity. This guide explains NHS eligibility, how it works, and your options for accessing it in the UK.
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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.
NHS Eligibility And Access For Semaglutide
NHS eligibility: You may qualify for semaglutide (Wegovy) on the NHS if you have a BMI of 30 kg/m² or above, or 27–29.9 kg/m² with at least one weight-related health condition such as type 2 diabetes, prediabetes, high blood pressure, or sleep apnoea. Adults of South Asian, Chinese, Black African, or Black Caribbean heritage may qualify at lower BMI thresholds (27.5 and above).
NHS access route: Semaglutide is prescribed through specialist tier 3 weight management services, not by your GP directly. You'll need a referral from your GP to a local NHS integrated care board (ICB) weight management service. NICE approved tirzepatide (and GLP-1 medications) for use within these services in 2024.
Availability: NHS provision varies significantly by region — some areas have long waiting lists (months to years), while others have limited or no access. Contact your GP to ask about your local services and waiting times.
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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.
Semaglutide Doses And Weight Loss Results
Semaglutide is given as a once-weekly injection, starting at 0.25 mg and escalating gradually to a maximum of 2.4 mg. Based on the STEP-1 clinical trial, participants on the full 2.4 mg dose lost an average of approximately 14.9% of their body weight over 68 weeks — though individual results vary significantly. Weight loss was achieved alongside a reduced-calorie diet and increased physical activity; semaglutide is not a standalone solution.
Try our free GLP-1 weight loss calculator to estimate potential weight loss at different doses, and use our BMI calculator to check your starting point.
NHS vs private access: NHS semaglutide prescribing is through tier 3 services (often with waiting lists), whereas private access is through GPhC-registered online pharmacies following an online clinical assessment — usually faster but at a cost. Private semaglutide typically costs £129–£300+ per month depending on dose. Both routes require a valid prescription from a UK-licensed prescriber and an assessment of your suitability.
Important: Semaglutide is prescription-only; it cannot be purchased without clinical assessment. Always consult your GP before considering any weight loss medication.
- 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.
Is semaglutide the same as Ozempic?
Both contain the same active ingredient (semaglutide), but Ozempic is licensed for type 2 diabetes at doses up to 2 mg, while Wegovy is licensed for weight management at up to 2.4 mg. Ozempic is not approved for weight loss in the UK — using it off-label for weight loss is not recommended. Always use the licensed product (Wegovy) for weight management.
How long does it take to see weight loss on semaglutide?
Most people begin to notice appetite suppression and modest weight loss within 2–4 weeks on semaglutide. Significant weight loss typically becomes apparent after 8–12 weeks as doses are gradually increased. Results vary between individuals, and weight loss continues throughout the treatment period as your dose escalates.
Can I get semaglutide on the NHS for weight loss?
Yes, if you meet NHS eligibility criteria (BMI 30+, or 27–29.9 with comorbidities) and are referred to a tier 3 specialist weight management service. However, NHS availability is extremely limited and varies by region — many areas have waiting lists of 6 months to several years. Your GP can advise you about local NHS services and waiting times.
What are the main side effects of semaglutide?
The most common side effects are nausea, diarrhoea, vomiting, constipation, and stomach pain. These are usually mild and often improve as your body adjusts. Serious side effects (severe stomach pain, gallbladder problems, serious allergic reactions) are rare but require immediate medical attention. Always report side effects to your prescriber.
Do I need to stay on semaglutide forever?
There is no set duration — semaglutide can be continued as long as it remains effective and you tolerate it well. Some people stop after reaching their goal weight; others continue long-term to maintain weight loss, as weight often returns if treatment is stopped. Your prescriber will review your progress and help you decide on duration.
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.