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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Immediate Weight Loss Pills: What's Available in the UK?
If you're looking for immediate weight loss pills in the UK, prescription medication options are available for eligible adults through both NHS and private routes. However, it's important to understand that effective weight management typically involves a combination of medication, dietary changes, and physical activity — there are no truly "immediate" solutions. The most commonly prescribed weight loss medications in the UK are Mounjaro and Wegovy, both of which require a clinical assessment before prescription. This guide explains what's available, who qualifies, and how to access these treatments through your GP or private prescribers.
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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.
UK-Licensed Prescription Weight Loss Options
Three prescription-only medications are currently licensed in the UK for weight management:
- Mounjaro (tirzepatide) — a once-weekly injection that works on two hormone pathways (GIP and GLP-1). In clinical trials, it helped adults lose an average of 15–21% of their body weight when combined with diet and exercise.
- Wegovy (semaglutide) — a once-weekly GLP-1 injection. Clinical evidence shows average weight loss of approximately 15% of body weight at the maximum dose.
- Saxenda (liraglutide) — a daily GLP-1 injection. This is an alternative for those who prefer different dosing or who have tried other options.
All three are prescription-only medicines requiring clinical assessment. Your GP or a licensed prescriber will assess your individual eligibility based on your BMI, health history, and weight-related conditions. Results vary between individuals, and these medications work best alongside a reduced-calorie diet and increased physical activity — not as a standalone solution.
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.
NHS Access vs Private Routes in the UK
NHS access: Prescription weight loss medication is available through specialist tier 3 weight management services, but access varies significantly by region. You'll typically need a GP referral, and waiting lists can be lengthy in many areas. Contact your GP to ask about NHS weight management services in your area.
Private access: Licensed UK prescribers can prescribe these medications following an online clinical assessment through GPhC-registered pharmacies. This route is faster but involves out-of-pocket costs (typically £130–£320 per month depending on dose). Both routes require a proper clinical assessment — there are no shortcuts to receiving prescription weight loss medication safely.
Use our free BMI calculator above to check your starting point, and discuss your eligibility with your GP or a licensed 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.
Can I get weight loss pills without a prescription in the UK?
No prescription weight loss medications can be legally dispensed in the UK without a prescription from a licensed prescriber. Some over-the-counter supplements exist, but they are not regulated or proven to the same standard as prescription medicines. Always consult your GP if you're considering weight loss treatment.
How quickly do prescription weight loss medications work?
Weight loss typically becomes noticeable within 4–8 weeks, but most significant results appear after 3–6 months of consistent use. These medications work gradually and sustainably — there are no "immediate" weight loss pills. Results depend on adherence to the medication, dietary changes, and physical activity.
Am I eligible for prescription weight loss medication on the NHS?
You may be eligible if you have a BMI of 30 or above, or 27 or above with weight-related health conditions (type 2 diabetes, high blood pressure, sleep apnoea, etc.). For South Asian, Chinese, Black African, or Black Caribbean adults, lower BMI thresholds apply. Ask your GP about specialist weight management services in your area.
What's the difference between Mounjaro and Wegovy for weight management?
Mounjaro is a dual GIP/GLP-1 agonist (works on two pathways) and showed average weight loss of 15–21% in clinical trials. Wegovy is a single GLP-1 agonist with average weight loss around 15%. Both are once-weekly injections. Your prescriber will assess which is more suitable for you based on your individual health profile.
Do I need to change my diet if I take weight loss medication?
Yes. Prescription weight loss medications are most effective when combined with a reduced-calorie diet and regular physical activity. These medications may help reduce appetite and cravings, but they work best as part of a comprehensive weight management plan, not alone.
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.