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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Best Weight Loss Pills That Work — What UK Evidence Shows
If you're searching for weight loss pills that actually work, the evidence in the UK points to prescription-only GLP-1 medications like Wegovy (semaglutide) and Mounjaro (tirzepatide). These are not effective pills — they work alongside diet and exercise — but clinical trials show they can support meaningful weight loss for eligible adults. Here's what you need to know about prescription weight management in the UK, how these medications work, and whether they might be right for you.
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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.
Which Weight Loss Pills Are Proven to Work?
In the UK, prescription weight loss medications have the strongest clinical evidence. Wegovy (semaglutide) is a GLP-1 receptor agonist — a once-weekly injection licensed for weight loss — that showed an average weight loss of approximately 15% of body weight in clinical trials. Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist, with clinical trials showing average weight loss between 15–21% depending on dose.
Non-prescription "weight loss pills" available over-the-counter (such as caffeine-based products or fibre supplements) show only modest effects — typically less than 2–3 kg weight loss — and work best as supplementary aids to diet and exercise, not standalone solutions.
- Prescription medications: Evidence-based, regulated by MHRA, require clinical assessment
- Over-the-counter supplements: Limited evidence, minimal weight loss, less regulated
- Fad diet pills: Often ineffective and potentially unsafe — avoid unregulated products
The key difference: prescription weight loss pills are clinically tested and require a prescriber to assess whether they're suitable for you.
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
If you have a BMI of 30 or above (or 27 or above with weight-related health conditions like type 2 diabetes or high blood pressure), you may be eligible for prescription weight loss medication. Access in the UK comes through two routes:
- NHS: Referral to a specialist tier 3 weight management service — availability varies by region, with waiting lists in many areas
- Private: Online consultation with a UK-licensed prescriber, followed by prescription through a GPhC-registered pharmacy
Try our free BMI calculator above to check your starting point, and our GLP-1 weight loss calculator to estimate potential results. Your GP or prescriber can then advise on which medication and approach suits your individual health needs.
- 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.
Do weight loss pills really work?
Prescription weight loss pills like Wegovy and Mounjaro have strong clinical evidence showing they can support meaningful weight loss — typically 15–21% of body weight — when combined with diet and exercise. Over-the-counter pills show much weaker evidence. Results vary between individuals, and medication works best as part of a broader weight management plan.
What's the difference between Wegovy and Mounjaro?
Both are prescription-only once-weekly injections. Wegovy (semaglutide) is a GLP-1 agonist; Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist. Clinical trials suggest Mounjaro may produce slightly higher average weight loss, but individual responses vary. Your prescriber will assess which is most suitable for you.
Can I get weight loss pills on the NHS?
Yes, if you're eligible and referred to a specialist tier 3 weight management service. Availability and waiting times vary significantly across the UK. Your GP can refer you, or you can access prescription medications privately through online prescribing services.
Are weight loss pills safe?
Prescription weight loss medications are regulated by the MHRA and have been tested for safety. Common side effects include nausea and digestive changes, usually mild and temporary. However, they're not suitable for everyone — a clinical assessment is essential. Always discuss any health conditions with your prescriber.
How much weight will I lose with weight loss pills?
Clinical trials show average weight loss of 15–21% of body weight with prescription GLP-1 medications, though individual results vary significantly. Weight loss typically occurs over 16–72 weeks and depends on your starting weight, dose, diet, and exercise. Our weight loss calculator can help estimate potential outcomes based on your profile.
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.