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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Fast Weight Loss Medicine in the UK
If you're looking for fast weight loss medicine in the UK, prescription-only medications like Mounjaro and Wegovy are clinically approved options for eligible adults. These GLP-1 and dual GIP/GLP-1 receptor agonist injections may help reduce appetite and support sustainable weight management alongside lifestyle changes. However, access depends on your BMI, health conditions, and whether you pursue NHS or private routes. Understanding your eligibility and how these medicines work is the first step toward making an informed decision with your GP.
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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-Licensed Weight Loss Medicines and How They Work
Three prescription-only weight loss medicines are currently licensed for use in the UK: Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). Mounjaro is a dual GIP and GLP-1 receptor agonist that activates two natural hormone pathways to help regulate appetite and reduce food cravings. Wegovy and Saxenda are GLP-1 agonists that work through a single hormone mechanism. In clinical trials, these medications helped participants achieve significant weight loss alongside reduced-calorie diet and increased physical activity—though individual results vary considerably. Mounjaro and Wegovy are injected once weekly, while Saxenda requires a daily injection. All three medications slow how quickly food leaves the stomach and increase feelings of fullness after smaller meals. Use our GLP-1 weight loss calculator to estimate potential outcomes at different doses based on clinical trial data.
- Mounjaro: Average 15–clinically studied weight loss over 72 weeks at maximum dose (clinical trial)
- Wegovy: Average clinically studied weight loss over 68 weeks (STEP-1 trial)
- Saxenda: Average 5–clinically studied weight loss; oldest licensed option
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 to Fast Weight Loss Medicine
NHS access: Weight loss medicines are prescribed through NHS specialist tier 3/4 weight management services, not standard GP prescriptions. You'll need a GP referral to these services, and availability varies significantly by region and ICB (Integrated Care Board). Waiting lists can be substantial in many areas. Private access: Available through GPhC-registered online pharmacies following a clinical assessment with a UK-licensed prescriber. Private prescribing doesn't require NHS referral but involves costs typically ranging from £129–£320 monthly depending on dose and provider. Either route requires a prescription—prescription weight loss medicine is not available over-the-counter. Start by speaking with your GP about whether you're eligible (BMI 30+ or BMI 27–29.9 with weight-related health conditions) and exploring available options in your area.
- 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 makes a weight loss medicine "fast-acting"?
Fast weight loss medicine doesn't mean gradual improvement—it means these medications help you lose weight more rapidly than diet and exercise alone. Mounjaro and Wegovy show measurable weight loss within weeks, with most significant results visible over 3–6 months. Results depend on dose, adherence, and lifestyle changes. Individual timelines vary considerably.
Am I eligible for prescription weight loss medicine in the UK?
Adults with a BMI of 30 or above, or 27–29.9 with weight-related health conditions like type 2 diabetes or high blood pressure, may be eligible. Eligibility thresholds are lower for adults of South Asian, Chinese, Black African, or Black Caribbean heritage (from BMI 27.5). Your GP or a licensed prescriber can assess your individual circumstances and eligibility.
Can I get fast weight loss medicine through the NHS?
Yes, but access is through specialist weight management services (tier 3/4), not standard GP prescription. You'll need a GP referral, and availability varies by region. Many areas have long waiting lists. Private prescribing is an alternative route that doesn't require NHS referral and may be faster, though it involves costs.
What are the side effects of fast-acting weight loss medicine?
Common side effects include nausea, diarrhoea, constipation, and stomach pain. These often improve over time as your body adjusts. Serious side effects are rare but can include pancreatitis or gallbladder issues. Always discuss potential side effects with your prescriber, and seek urgent medical attention for severe persistent stomach pain.
How can I check if fast weight loss medicine is right for me?
Start by calculating your BMI using our free BMI calculator to understand your health category. Then speak with your GP about whether prescription weight loss medication aligns with your health goals and circumstances. Your GP can discuss eligibility, NHS availability in your area, or refer you to appropriate specialist services or private assessment options.
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.