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 Weight Loss Side Effects: Cost & Access in the UK
Semaglutide is a GLP-1 receptor agonist prescribed in the UK as Wegovy for weight management. Before considering this weekly weight loss injection, it's important to understand both the potential side effects and how to access it — whether through the NHS or private prescription. This guide covers what semaglutide side effects to expect, UK pricing, and the different routes to getting a prescription.
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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.
Semaglutide Side Effects and UK Private Cost
As a GLP-1 receptor agonist, semaglutide (Wegovy) works by reducing appetite and helping you feel fuller after smaller meals. Common side effects include nausea, diarrhoea, vomiting, and stomach pain — particularly when starting or increasing doses. Most side effects are mild to moderate and often improve within a few weeks as your body adjusts.
UK private prescription costs: Wegovy typically costs between £150–£300 per month depending on your dose and the online clinic provider. Starting doses (0.25–0.5 mg) are usually cheaper than maintenance doses (1.7–2.4 mg). Prices vary because different GPhC-registered pharmacies set their own fees for prescriptions and consultations. Initial online consultations usually cost £30–£50, though some providers include this in the monthly fee.
Individual results vary significantly — clinical trials showed average weight loss of around 15% body weight, but this was alongside a reduced-calorie diet and increased physical activity. Always budget for ongoing costs: weight loss medication is typically a long-term commitment, not a one-off course.
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 vs Private Access and How to Get Started
NHS route: Free on prescription, but access is through specialist tier 3 weight management services. You'll need a GP referral, and waiting lists can be months or years depending on your region. Availability varies significantly across different ICBs (Integrated Care Boards).
Private route: Faster access — typically within days. You'll have an online consultation with a UK-licensed prescriber, answer health questions, and receive a prescription if approved. You can then collect from a GPhC-registered pharmacy. No NHS referral needed. Try our GLP-1 weight loss calculator above to explore potential outcomes at different semaglutide doses, and use the BMI calculator to understand your starting point. Most private providers require you to be aged 18+, have a BMI of 30+ (or 27+ with weight-related health conditions), and declare any relevant medical history.
Before starting any semaglutide 2.4mg dose, inform your prescriber of all medications — semaglutide may affect absorption of oral contraceptives and diabetes medications. If you experience severe stomach pain (possible pancreatitis), serious allergic reactions, or unexplained vision changes, seek urgent medical attention. Weight loss with semaglutide is not assured; individual results vary based on adherence, diet, and lifestyle changes.
- 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 are the most common semaglutide side effects?
Nausea, diarrhoea, vomiting, constipation, and stomach pain are very common, especially when starting or increasing doses. Most improve within 2–4 weeks. Injection site reactions, headache, and fatigue are also common. Serious side effects are rare but include severe stomach pain (possible pancreatitis) and serious allergic reactions — seek immediate medical attention if these occur.
How much does Wegovy cost privately in the UK?
Private Wegovy costs typically range from £150–£300 per month depending on the dose and provider. Starting doses cost less than maintenance doses. Online consultation fees vary from £30–£50, though some providers include this in the monthly subscription. Always check the total cost with your chosen provider before starting.
Can I get Wegovy on the NHS in the UK?
Yes, semaglutide (Wegovy) is approved for NHS use, but only through specialist tier 3 weight management services. You'll need a GP referral. Availability and waiting times vary significantly by region — some areas have long waiting lists. Ask your GP about local services and eligibility.
How do I get a private semaglutide prescription in the UK?
Register with a GPhC-registered online clinic, complete a health questionnaire, have an online consultation with a UK-licensed prescriber, and receive a prescription if approved. The process typically takes 24–48 hours. Your prescription is then dispensed by a registered pharmacy. You'll need to demonstrate BMI eligibility and declare relevant medical history.
Is semaglutide the same as Ozempic?
Both contain the same active ingredient (semaglutide), but Ozempic is licensed for type 2 diabetes (doses up to 2 mg) and is not licensed for weight loss in the UK. Wegovy is the licensed weight management version with a maximum dose of 2.4 mg. Using Ozempic for weight loss would be off-label prescribing.
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.