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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Quick Weight Loss Drugs Available in the UK
If you're looking for quick weight loss drugs in the UK, prescription medications are available for eligible adults through both NHS and private prescribing. The main options are Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide) — all licensed weight management medications that work alongside lifestyle changes. This guide explains what these medications are, who can access them, and how the UK healthcare system approaches prescription weight loss treatment. Understanding your options is the first step toward finding the right approach for your weight management goals.
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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.
UK-Licensed Weight Loss Medications Explained
Three prescription weight loss medications are currently licensed in the UK for weight management:
- Mounjaro (tirzepatide) — a once-weekly injection that activates dual GIP and GLP-1 pathways. Clinical trials showed participants lost an average of 15–21% of body weight when combined with dietary changes and physical activity.
- Wegovy (semaglutide) — a once-weekly GLP-1 injection. Evidence suggests average weight loss of around 14.9% of body weight in clinical trials.
- Saxenda (liraglutide) — a daily GLP-1 injection, typically prescribed when once-weekly options are unsuitable.
All three are prescription-only medicines requiring clinical assessment. Use our free GLP-1 weight loss calculator to explore potential outcomes at different doses. Individual results vary significantly based on lifestyle changes, adherence, and personal health factors. These medications are designed to support, not replace, reduced-calorie diet and increased physical activity.
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 — Getting Prescription Weight Loss Treatment
NHS access: Weight loss medications are available through specialist tier 3 and tier 4 weight management services. You'll need a referral from your GP and meet eligibility criteria (typically BMI ≥30, or ≥27 with weight-related health conditions). Availability and waiting times vary significantly by region. Calculate your personal BMI using our free BMI calculator to understand your eligibility baseline.
Private access: Licensed prescribers offer online consultations with a clinical assessment. If suitable, prescriptions are dispensed by GPhC-registered pharmacies. Private options are available without NHS referral, typically costing £129–£320 monthly depending on dose.
Next step: Speak with your GP about prescription weight loss medication options. They can assess your individual circumstances and discuss whether GLP-1 or GIP/GLP-1 medications are appropriate for you.
- 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 is the fastest-working weight loss medication available in the UK?
Mounjaro (tirzepatide) showed the fastest average weight loss in clinical trials at higher doses, but "fastest" varies by individual. Results depend on dose escalation, lifestyle changes, and personal metabolism. Your GP can advise which option suits your situation best. Never prioritise speed over safety — sustainable weight loss is typically 0.5–1 kg per week.
Can I get quick weight loss drugs on the NHS?
Yes, if you meet eligibility criteria (BMI ≥30, or ≥27 with weight-related conditions). Access is through specialist weight management services via GP referral. However, NHS waiting lists can be lengthy — availability varies by region and local integrated care board (ICB) capacity.
How much weight will I lose with prescription weight loss medication?
Clinical trials showed average losses of 15–21% of body weight with Mounjaro and 14.9% with Wegovy over 12–18 months — but individual results vary. Some people lose more, others less. Weight loss depends on dose, adherence, dietary changes, and physical activity. Use our GLP-1 weight loss calculator for a personalised projection.
Are quick weight loss drugs safe?
UK-licensed medications (Mounjaro, Wegovy, Saxenda) have undergone rigorous safety testing. Common side effects include nausea and digestive changes, typically mild and temporary. Serious side effects are rare but possible. All require prescription and clinical assessment — your prescriber will evaluate whether the medication is safe for you based on your health history.
Do I need to change my diet if I take weight loss medication?
Yes. These medications are most effective when combined with reduced-calorie diet and increased physical activity. They support appetite regulation and feeling fuller, making dietary changes easier — but medication alone won't produce lasting weight loss without lifestyle changes. This is why NHS guidance emphasises lifestyle support alongside medication.
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.