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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How to Take Semaglutide — Step-by-Step UK Guide
Semaglutide is a GLP-1 receptor agonist available in the UK as Wegovy for weight management. This guide explains how to take semaglutide injections properly, from your first dose through maintenance treatment. If you're considering semaglutide weight loss treatment, understanding the injection technique, dosing schedule, and access routes is essential. This information is for educational purposes — always follow your prescriber's instructions and consult your GP if you have questions about your treatment.
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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.
How to Take Semaglutide — Injection Technique and Dosing Schedule
Semaglutide (Wegovy) is administered as a once-weekly subcutaneous injection using a pre-filled auto-injection pen. Each pen contains one dose and is injected under the skin (subcutaneously) rather than into muscle or vein.
- Starting dose: 0.25 mg once per week for weeks 1–4
- Week 5–8: Increase to 0.5 mg once per week
- Week 9–12: Increase to 1 mg once per week
- Week 13–16: Increase to 1.7 mg once per week
- Week 17+: Maintenance at 2.4 mg once per week (maximum dose)
Each dose increase should occur at weekly intervals — minimum 7 days between injections. Your prescriber may adjust your schedule based on tolerability. Clinical trials showed that at 2.4 mg, semaglutide supports an average weight loss of approximately 14.9% body weight, though individual results vary significantly.
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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.
Cost and Access Routes for Semaglutide in the UK
NHS access: Semaglutide (Wegovy) is available through NHS specialist weight management services (tier 3). This requires a GP referral and assessment by a specialist team. Availability varies significantly by region, and waiting lists can be lengthy in many areas.
Private access: Semaglutide is available through UK-licensed online prescribers. Private prescription costs typically range from £129–£250 per month depending on the dose, with higher maintenance doses (1.7 mg and 2.4 mg) towards the upper end. Access is via online consultation — no NHS referral needed. Use our GLP-1 weight loss calculator to estimate potential results at different doses and plan your budget accordingly.
- 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.
Where should I inject semaglutide?
Semaglutide is injected subcutaneously (under the skin) in the stomach area (abdomen), upper thigh, or upper arm. Rotate injection sites each week to prevent skin irritation. Most users find the abdomen easiest for self-injection. Your prescriber will demonstrate the correct technique during your initial consultation.
Can I switch from Ozempic to Wegovy?
Ozempic contains semaglutide but is approved only for type 2 diabetes (doses up to 2 mg). Wegovy is the licensed weight management formulation (up to 2.4 mg). Switching requires a new prescription and prescriber assessment. Never switch medications without medical guidance — your dose may change during the transition.
What happens if I miss a semaglutide injection?
If you miss a dose within 4 days, take it as soon as you remember and continue your normal weekly schedule. If more than 4 days have passed, skip that dose and inject on your regular scheduled day. Never double-dose. Maintain at least 72 hours (3 days) between injections.
How do I store semaglutide pens?
Unopened pens must be stored in a refrigerator at 2–8°C in their original carton to protect from light — do not freeze. After first use, pens can be stored at room temperature (below 30°C) for up to 30 days. Dispose of pens 30 days after first use. Always check the expiry date before using.
Do I need blood tests before starting semaglutide?
Yes. Before prescription, your prescriber will typically request baseline health information and may recommend blood tests to check liver function, kidney function, and blood sugar levels. This ensures semaglutide is safe for you and helps identify any underlying conditions. Your GP can arrange these tests if needed.
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.