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
Weight Loss Pill That Actually Works — What the Evidence Shows
If you're searching for a weight loss pill that actually works, you're looking at prescription medications licensed in the UK — not over-the-counter tablets. The most effective prescription weight loss medications are GLP-1 receptor agonists like Wegovy (semaglutide), which showed an average weight loss of around 15% of body weight in clinical trials. These aren't effective pills; they work alongside dietary changes and physical activity. This guide explains which medications have solid clinical evidence, how they work, and how to access them through the NHS or private prescription in the UK.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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.
Which Weight Loss Medications Actually Work in the UK?
The most rigorously tested weight loss medications available in the UK are prescription-only GLP-1 receptor agonist injections. Wegovy (semaglutide) is a once-weekly injection licensed for weight management in UK adults. In the STEP-1 clinical trial, participants taking Wegovy alongside a reduced-calorie diet lost an average of 14.9% of their body weight over 68 weeks — compared to just 2.4% in the placebo group. Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist that showed slightly higher average weight loss (around 15–21% body weight) in the SURMOUNT clinical trials.
These medications may help regulate appetite, reduce food cravings, and support feeling fuller after smaller meals. They are not the same as over-the-counter weight loss supplements or tablets, which have limited clinical evidence. Individual results vary significantly — some people lose more, some less — and these medications work best when combined with lifestyle changes. Use our free GLP-1 weight loss calculator to estimate potential weight loss at different doses, or calculate your BMI using our free BMI calculator to assess your eligibility.
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.
How to Access Weight Loss Medication in the UK
NHS access: Prescription weight loss medication is available through NHS specialist weight management services (tier 3) if you have a BMI of 30 or above, or 27–29.9 with weight-related health conditions like type 2 diabetes or hypertension. Your GP can refer you, though waiting times vary by region and can be lengthy.
Private access: GLP-1 medications are available through GPhC-registered online pharmacies following a consultation with a UK-licensed prescriber. This typically costs £129–£320 per month depending on dose. All prescription weight loss medication requires a clinical assessment to ensure it's safe for you. Results depend on adherence to the treatment plan, dietary changes, and increased physical activity. Track your progress using our free progress tracker.
- 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 there a weight loss pill that actually works without diet and exercise?
No. All evidence-based weight loss medications work best alongside a reduced-calorie diet and increased physical activity. Clinical trials show that without these lifestyle changes, weight loss is significantly reduced. Medications support these changes but are not replacements for them.
What's the difference between Wegovy and Ozempic for weight loss?
Both contain semaglutide, but Ozempic is licensed for type 2 diabetes management (up to 2mg). Wegovy is the licensed weight management version (up to 2.4mg) and is specifically approved for weight loss in the UK. Ozempic is not licensed for weight loss and using it off-label for this purpose is not recommended.
How much weight can you lose with prescription weight loss pills?
Clinical trials show average weight loss of 14–21% of body weight over 68 weeks, depending on the medication and dose. However, individual results vary widely. Some people lose more, some less. Rate of weight loss typically slows after 6–12 months and results depend on adherence and lifestyle changes.
Are weight loss pills available on the NHS?
Yes, through NHS specialist weight management services if you meet eligibility criteria (BMI ≥30, or ≥27 with weight-related health conditions). Access varies significantly by region and waiting lists can be very long. Your GP can refer you, or you can access prescription weight loss medication privately.
What are the side effects of prescription weight loss pills?
The most common side effects are nausea, diarrhoea, constipation, and stomach pain, especially in the first few weeks. These often improve over time. Serious side effects are rare but include severe stomach pain (possible pancreatitis), gallbladder problems, and serious allergic reactions. Always discuss risks with your prescriber.
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.