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
Free tracker included with every download this week
How Semaglutide Works for Weight Loss
Semaglutide is a prescription-only weight loss injection licensed for use in the UK under the brand name Wegovy. It works by activating the GLP-1 receptor, a natural hormone pathway that helps regulate appetite and blood sugar control. Clinical trials showed that semaglutide, combined with a reduced-calorie diet and increased physical activity, may help adults lose an average of around 15% of their body weight over 68 weeks. Individual results vary significantly, and semaglutide is not suitable for everyone. Your GP or a licensed prescriber will assess whether it's appropriate for you based on your personal health.
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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 Semaglutide Works and What It Does
Semaglutide is a GLP-1 receptor agonist — it mimics glucagon-like peptide-1, a natural hormone your body produces after eating. When you activate the GLP-1 pathway, several things happen:
- Appetite signals: The medication sends signals to your brain that you feel fuller sooner, reducing hunger and food cravings
- Slower digestion: Food moves through your stomach more gradually, helping you feel satisfied after smaller meals
- Blood sugar control: Semaglutide helps regulate blood sugar levels, which can reduce energy crashes and cravings
It is not insulin and does not work the same way as insulin medications. Semaglutide (Wegovy) is manufactured by Novo Nordisk and is a once-weekly injectable medicine. When used alongside lifestyle changes — reduced-calorie diet and increased physical activity — it may support sustainable weight loss. However, it is a prescription-only medication and requires clinical assessment before being prescribed.
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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, Eligibility, and What to Expect
Semaglutide (Wegovy) is prescribed in increasing weekly doses, starting at 0.25 mg and escalating to a maximum of 2.4 mg per week. Your prescriber will increase your dose every 1–2 weeks based on how you tolerate the medication. In the UK, you may be eligible for semaglutide if you have a BMI of 30 or above, or 27–29.9 with a weight-related health condition such as type 2 diabetes, high blood pressure, or cardiovascular disease. Lower BMI thresholds may apply if you are of South Asian, Chinese, Black African, or Black Caribbean heritage. Common side effects include nausea, diarrhoea, constipation, and stomach pain — most improve after the first few weeks. Our GLP-1 weight loss calculator can help you estimate potential outcomes, and use our BMI calculator to check your current BMI and understand whether you might be eligible for treatment.
- 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 Wegovy and Ozempic contain semaglutide, but they are different medicines. Ozempic is licensed for type 2 diabetes management and contains up to 2 mg of semaglutide. Wegovy is specifically licensed for weight management and contains up to 2.4 mg. Using Ozempic for weight loss is off-label in the UK. Wegovy is the correct licensed choice for weight loss.
How much weight can I lose with semaglutide?
In the STEP-1 clinical trial, participants taking 2.4 mg semaglutide lost an average of approximately 14.9% of their body weight over 68 weeks, alongside a reduced-calorie diet and increased physical activity. Individual results vary significantly — some people lose less, some lose more. Results depend on your starting weight, adherence to lifestyle changes, and individual metabolism.
What are the main side effects of semaglutide (Wegovy)?
The most common side effects are nausea, diarrhoea, constipation, and stomach pain. These are usually mild to moderate and tend to improve after the first few weeks as your body adjusts. Serious side effects are rare but can include severe abdominal pain (possible pancreatitis) or gallbladder problems. Always report persistent or severe symptoms to your prescriber.
How do I access semaglutide (Wegovy) in the UK?
Semaglutide is available through NHS specialist tier 3 weight management services (though availability varies by region and waiting lists can be long) or through private online prescribing following a clinical assessment. A UK-licensed prescriber will assess your eligibility, which includes BMI and health history. It is a prescription-only medicine and requires a prescription from a qualified healthcare professional.
How does semaglutide compare to other weight loss injections?
Semaglutide (Wegovy) is a GLP-1 receptor agonist. Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist, which may work via two pathways instead of one. In clinical trials, tirzepatide showed slightly higher average weight loss (up to 20.9%) compared to semaglutide (14.9%), but individual results vary. Both are prescription-only and require clinical assessment.
Ready to take control of your weight loss journey?
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