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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Losing Weight Pills — What Works in the UK?
Losing weight pills are prescription-only medications that may help support weight management alongside diet and exercise. In the UK, several licensed weight loss pills and injections are available through NHS specialist services or private prescription. This guide explains how they work, who might be eligible, and how they fit into a sustainable weight management approach.
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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.
Types of Prescription Weight Loss Medications
The UK has approved several prescription weight loss medications, each working through different mechanisms to support sustainable weight loss. GLP-1 receptor agonists like Wegovy (semaglutide) work by activating natural hormone pathways that help regulate appetite and reduce food cravings. Semaglutide, used at the 2.4 mg dose in Wegovy, showed in clinical trials that participants lost an average of around 15% of their body weight when combined with a reduced-calorie diet and increased physical activity.
Another option is Mounjaro (tirzepatide), a dual GIP and GLP-1 receptor agonist that activates two hormone pathways simultaneously. Clinical trial data showed Mounjaro helped participants achieve average weight loss of 15–21% of body weight, though individual results vary significantly. A third licensed option is Saxenda (liraglutide), a GLP-1 injection given daily rather than weekly.
All prescription weight loss medications in the UK are prescription-only and require a clinical assessment before being prescribed. They are not suitable for everyone and work best when combined with lifestyle changes.
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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 Medications in the UK
Accessing prescription weight loss pills in the UK depends on your chosen route. Through the NHS, you can ask your GP for a referral to a tier 3 or tier 4 specialist weight management service. These services provide comprehensive assessments and prescribe medications where appropriate, though waiting lists vary significantly by region—some areas have very long waits.
Alternatively, private online prescribing is available through registered UK healthcare providers. After an online clinical consultation, a licensed prescriber can issue a prescription if the medication is deemed suitable for you. This route doesn't require an NHS referral and allows faster access, though there is a cost involved.
Whichever route you choose, sustainable weight loss depends on combining medication with lifestyle changes: reduced-calorie eating (aim for a 500 kcal deficit daily to lose approximately 0.5 kg per week) and increased physical activity. Use our free GLP-1 weight loss calculator to estimate potential outcomes at different doses.
- 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 pills available on the NHS?
Yes. Several prescription weight loss medications are approved by NICE for NHS use, including Mounjaro, Wegovy, and Saxenda. Access is through specialist tier 3 or tier 4 weight management services via GP referral. Availability and waiting times vary significantly by region. Your GP can discuss eligibility and refer you if appropriate.
How much weight can you lose with weight loss pills?
Results vary individually. Clinical trials showed GLP-1 medications help people lose 14–21% of body weight on average over 68–72 weeks, combined with diet and exercise. The NHS advises expecting loss of around 0.5–1 kg per week with sustained lifestyle changes. Individual outcomes depend on starting weight, adherence, diet, and activity level.
What are the side effects of weight loss pills?
Common side effects include nausea, diarrhoea, constipation, stomach pain, and fatigue—particularly during dose increases. Most side effects tend to reduce over time. Serious side effects are rare but can include severe stomach pain (possible pancreatitis) or gallbladder issues. Always discuss side effects with your prescriber.
Do weight loss pills work without diet and exercise?
No. Weight loss medications work best combined with a reduced-calorie diet and increased physical activity. They support appetite regulation and help you feel fuller, but they're not a substitute for lifestyle changes. The NHS recommends treating them as one part of a comprehensive weight management approach alongside behavioural support.
How long can you take weight loss pills?
Duration depends on your medication and individual circumstances. Some people take them long-term to maintain weight loss, while others use them short-term. Your prescriber will advise how long treatment is appropriate for you. If you stop medication, weight can return without sustained lifestyle changes, so combining pills with lasting diet and exercise habits is essential.
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.