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
What Weight Loss Pills Actually Work?
Weight loss pills that work in the UK are prescription-only medications backed by clinical evidence. The main options are GLP-1 receptor agonists like Wegovy (semaglutide) and Mounjaro (tirzepatide), which help reduce appetite and support weight management alongside lifestyle changes. These aren't quick fixes — they require a clinical assessment, work best with a reduced-calorie diet and increased physical activity, and results vary between individuals. Understanding how they work and what the evidence shows can help you decide if prescription weight loss medication might be right for you.
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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.
How Do Prescription Weight Loss Pills Work?
GLP-1 receptor agonists like Wegovy activate the GLP-1 hormone pathway in your body, which naturally signals appetite control and fullness. These medications may help reduce food cravings, support feeling satisfied after smaller meals, and slow how quickly food leaves your stomach. Mounjaro (tirzepatide) works differently — it's a dual GIP and GLP-1 agonist, meaning it activates two hormone pathways for potentially stronger appetite suppression.
Clinical trials show these medications can support meaningful weight loss when combined with lifestyle changes:
- Wegovy: Clinical evidence shows average weight loss of approximately 14.9% of body weight over 68 weeks in STEP trials
- Mounjaro: SURMOUNT trials demonstrated average weight loss ranging from 15% to 21% depending on dose, with the 15mg dose showing the strongest results
However, individual results vary significantly. These are prescription-only medicines requiring a clinical assessment to establish eligibility and monitor safety.
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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.
UK Access and What Makes a Weight Loss Pill "Work"
In the UK, prescription weight loss medication is available through NHS specialist tier 3 weight management services (with regional variation and waiting lists) or through private online prescribing. Eligibility typically requires a BMI of 30 or above, or 27 or above with weight-related health conditions like type 2 diabetes, high blood pressure, or sleep apnoea.
A weight loss pill truly "works" when it helps you lose weight sustained alongside diet and exercise — not as a standalone solution. Use our free GLP-1 weight loss calculator to estimate potential results at different doses. Check your personal eligibility with our BMI calculator to see whether you fall into the weight range where prescription medication may be considered by a prescriber.
- 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 work without diet and exercise?
Clinical evidence shows prescription weight loss pills like Wegovy and Mounjaro are most effective when combined with a reduced-calorie diet and increased physical activity. While these medications do help reduce appetite, sustainable weight loss requires lifestyle changes. A prescriber will always recommend diet and exercise alongside medication.
What's the difference between Wegovy and Mounjaro?
Wegovy (semaglutide) is a GLP-1 agonist activating one hormone pathway. Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist activating two pathways, which may support slightly stronger appetite suppression. Both require prescriptions. Clinical trials show Mounjaro users lost approximately 15–21% of body weight versus approximately 14.9% for Wegovy, though individual results vary.
Are weight loss pills available on the NHS?
Yes, prescription weight loss medication is available through NHS specialist weight management services (tier 3). However, access varies significantly by region, and waiting lists can be lengthy. Private online prescribing is also available in the UK. Your GP can discuss which option is appropriate for your circumstances.
How long do you need to take weight loss pills?
This varies individually. Some people use weight loss medication short-term to reach a target weight, then stop. Others continue long-term for ongoing weight management. A prescriber will assess your individual situation and discuss how long treatment may be needed. Stopping medication may result in weight regain if lifestyle changes aren't maintained.
What counts as a "healthy weight loss" goal?
The NHS recommends losing 0.5 to 1 kg per week for sustainable results. Even a 5–10% reduction in body weight can bring meaningful health benefits including improved blood sugar control, lower blood pressure, and reduced joint strain. Calculate your healthy weight range using our free BMI calculator to see what target makes sense for your height.
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.