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 Plans: UK Prescription Medication Options
If you're looking for fast weight loss plans in the UK, prescription medications can be an option for eligible adults. Mounjaro, Wegovy, and Saxenda are licensed weight management medications available through NHS specialist services or private prescribing. This guide explains how these prescription weight loss options work, who can access them, and the evidence behind their effectiveness. Use our free GLP-1 weight loss calculator to estimate potential results, and consult your GP to find out if you're eligible for prescription support.
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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 Medications Explained
Mounjaro (tirzepatide) and Wegovy (semaglutide) are the most commonly prescribed weight management medications in the UK. Both are once-weekly injections that work by mimicking natural hormones that regulate appetite and blood sugar.
Clinical evidence: In trials, Mounjaro helped participants lose an average of 15–21% of their body weight, while Wegovy supported losses of around 15% on average. Saxenda (liraglutide) is an older GLP-1 option requiring daily injections, with similar effectiveness.
Eligibility: You may be eligible if you have a BMI of 30 or above, or BMI of 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or sleep apnoea. For adults of South Asian, Chinese, Black African, or Caribbean heritage, lower BMI thresholds apply due to higher metabolic risk.
How they work: These medications slow gastric emptying, reduce appetite signals to the brain, and help you feel fuller after smaller meals. Results are best when combined with reduced-calorie diet and increased physical activity.
Use our BMI calculator above to check if you fall within the eligible range for prescription weight management.
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: How to Get Started
NHS access: Referral to a tier 3 specialist weight management service through your GP is the NHS route. Availability and waiting times vary significantly by region—some areas have substantial waiting lists. Your GP can assess whether specialist referral is appropriate for your circumstances.
Private access: GPhC-registered online prescribing services can assess eligibility and issue prescriptions without NHS referral. This route is faster but involves private costs (typically £129–£320+ per month depending on dose).
Next steps: Schedule a conversation with your GP to discuss weight management options. They can refer you to specialist services, discuss eligibility, and advise on the most suitable approach for your health situation. Track your weight management journey using our free progress tracker, which helps monitor results over time.
- 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.
Are weight loss injections like Mounjaro actually fast?
Weight loss injections are effective but not "fast" in the short term. Average weight loss is 0.5–1 kg per week, similar to other methods. However, over months, participants in trials lost 15–21% of body weight. Results vary individually and require lifestyle changes alongside medication.
Can I get Mounjaro or Wegovy on the NHS?
Yes, but access is through specialist tier 3 weight management services following GP referral. Availability varies by region. Some areas have long waiting lists. Private prescribing offers faster access. Your GP can advise on your local NHS options.
What's the difference between Mounjaro and Wegovy?
Mounjaro uses a dual hormone mechanism (GIP + GLP-1), while Wegovy is GLP-1 only. Mounjaro goes up to 15 mg weekly; Wegovy up to 2.4 mg. Clinical trials show slightly higher average weight loss with Mounjaro, though individual results vary significantly.
Do I have to take weight loss medication forever?
There's no fixed answer—it depends on your health goals and what your prescriber recommends. Some people continue long-term; others stop after reaching targets. Weight often returns if medication stops without sustained lifestyle changes. Discuss long-term plans with your GP.
What side effects should I expect?
Common side effects include nausea, diarrhoea, constipation, and stomach pain—usually mild and temporary. Most people adjust within weeks. Serious side effects are rare but can include pancreatitis symptoms or gallbladder issues. Report persistent symptoms to your prescriber immediately.
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.