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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Weight Loss Pills To Lose Weight Fast: What Works in the UK
If you're looking for weight loss pills to lose weight fast, you should know that effective prescription weight loss medications are available in the UK—but "fast" depends on what's realistic for your health. Weight loss injections like Wegovy (semaglutide) and Mounjaro (tirzepatide) are prescription-only medicines that can help support weight loss when combined with diet and exercise changes. The NHS recommends losing weight at a rate of 0.5 to 1 kg per week for sustainable results. This guide explains how these medications work, who can access them, and what to expect from weight loss treatment in the UK.
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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 Prescription Weight Loss Medications Work
Weight loss pills and injections available in the UK work by affecting your appetite and how your body regulates blood sugar. Wegovy (semaglutide) is a once-weekly GLP-1 injection that activates hormones in your brain to reduce hunger and help you feel fuller after smaller meals. Mounjaro (tirzepatide) works similarly but with dual action—targeting both GLP-1 and GIP pathways for potentially stronger appetite suppression.
In clinical trials, these medications helped patients lose an average of 14–21% of their body weight over 68–72 weeks, alongside a reduced-calorie diet and increased physical activity. Individual results vary significantly. Both are prescription-only and require a clinical assessment to check they're suitable for you. They're injected once weekly at home and are not the same as oral diet pills.
- Wegovy: GLP-1 agonist, up to 2.4 mg weekly
- Mounjaro: GIP + GLP-1 agonist, up to 15 mg weekly
- Both require prescription from a UK-licensed prescriber
- Results take weeks to months—not days
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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.
Where To Access Weight Loss Medication in the UK
NHS access: Weight loss medications are prescribed through specialist tier 3 weight management services. You'll need a GP referral and meet NHS eligibility criteria (BMI 30+ or BMI 27–29.9 with weight-related health conditions). NHS availability varies by region, and waiting lists can be lengthy.
Private access: GPhC-registered online prescribers offer these medications following a virtual consultation. If clinically appropriate, you'll receive a prescription and the medication is dispensed by a UK pharmacy. This route is faster than NHS but involves private costs (typically £129–£320+ per month depending on dose).
Before starting any weight loss medication, use our free BMI calculator to understand your current BMI and where you sit relative to NHS guidelines. Your prescriber will assess your individual health and confirm whether treatment is right 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.
Can weight loss pills make you lose weight fast without diet changes?
No. Prescription weight loss medications like Wegovy and Mounjaro are designed to support weight loss alongside a reduced-calorie diet and increased physical activity—not replace these changes. In clinical trials, the most effective results combined medication with lifestyle modifications. Medication helps reduce appetite and cravings, but you still need to make dietary choices and move more.
What's the difference between Wegovy and Mounjaro?
Wegovy (semaglutide) is a GLP-1 agonist with average weight loss around 14–15% of body weight. Mounjaro (tirzepatide) is a dual GIP + GLP-1 agonist with average weight loss around 15–21% of body weight in trials. Both are once-weekly injections, but Mounjaro's dual mechanism may offer stronger appetite suppression. Individual results vary, and your prescriber will advise which is suitable for you.
How long does it take to see weight loss results with these medications?
Weight loss typically begins within 2–4 weeks, but results accelerate over weeks 4–12 as your dose increases. By 12–16 weeks, most people notice meaningful weight loss. Clinical trials measured results over 68–72 weeks. The NHS recommends patience—sustainable weight loss is 0.5–1 kg per week. "Fast" is relative; these medications support gradual, lasting weight loss, not crash dieting.
Are weight loss pills available on the NHS?
Yes. Wegovy and Mounjaro are available on the NHS through specialist weight management services (tier 3). You need a GP referral and must meet eligibility criteria: BMI 30+ or BMI 27–29.9 with weight-related health conditions. NHS access varies by region. Private access is also available through online prescribers without waiting lists.
What are the side effects of weight loss medications?
Common side effects include nausea, diarrhoea, vomiting, and constipation—typically most noticeable in the first 2–4 weeks and often improve as your body adjusts. Serious side effects are rare but include severe stomach pain (possible pancreatitis) or allergic reactions. Your prescriber will discuss full risks during your assessment and monitor you during treatment.
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.