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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Six Week Weight Loss: Prescription Medication Options in the UK
Losing weight in six weeks requires a structured approach. For eligible adults in the UK, prescription weight management medication may offer support alongside diet and exercise. This guide covers the prescription options available through the NHS and privately, who can access them, and what realistic expectations are for a six-week timeframe. Weight management in the UK is supported by multiple evidence-based approaches, from lifestyle changes to clinical medications. Understanding your options helps you make an informed decision with your GP.
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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 Weight Loss Medications
Three prescription-only weight loss injections are currently licensed in the UK for weight management: Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide).
- Mounjaro: Once-weekly injection, dual GIP and GLP-1 agonist. Clinical trials showed average weight loss of 15–21% over 72 weeks alongside reduced-calorie diet and exercise.
- Wegovy: Once-weekly injection, GLP-1 agonist. STEP trial data showed approximately 15% average weight loss at 68 weeks.
- Saxenda: Daily injection, GLP-1 agonist. Available on NHS in some regions, more commonly accessed privately.
All three require a clinical assessment by a licensed prescriber. Eligibility generally requires a BMI of 30 or above, or 27 or above with weight-related health conditions such as type 2 diabetes, high blood pressure, or cardiovascular disease. For six-week outcomes specifically, results vary widely—these medications work best as part of longer-term weight management (typically 12+ weeks), but some users report noticeable appetite reduction and early weight changes within four to six weeks.
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 vs Private Access in Six Weeks
NHS access: GLP-1 weight loss medications are available through specialist tier 3 weight management services. Referral from your GP is required, and waiting times vary significantly by region—many areas have lists of several months. If you wish to explore NHS options, speak with your GP about referral to your local weight management service.
Private access: All three medications are available through private prescribing services. A remote clinical assessment by a UK-licensed prescriber determines eligibility. Private access avoids NHS waiting lists but involves out-of-pocket costs (typically £129–£320 per month depending on dose). For a six-week outcome, starting private prescription today means you could begin medication within days, whereas NHS referral could take months. Either route requires commitment to diet and exercise changes for meaningful results.
- 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 lose weight in six weeks with prescription medication?
Weight loss medication may support weight reduction within six weeks, but results vary. Some users notice appetite changes and early weight loss within 4–6 weeks. However, clinical trials measure outcomes over 12+ weeks. Medication works best alongside a reduced-calorie diet and regular physical activity. Realistic expectations: 2–5 kg loss in six weeks is possible with medication plus lifestyle changes, though individual results vary significantly.
How do I know if I'm eligible for weight loss medication in the UK?
You may be eligible if you have a BMI of 30 or above, or 27 or above with a weight-related health condition (type 2 diabetes, high blood pressure, cardiovascular disease, or sleep apnoea). Use our free BMI calculator above to check your current BMI. After calculating, your next step is a conversation with your GP or a licensed prescriber who can assess your individual health and confirm eligibility.
How quickly can I start prescription weight loss medication?
Through the NHS, referral to specialist services can take weeks or months depending on your region. Through private prescribing, a clinical assessment can be completed within 24–48 hours, with medication dispensed shortly after if approved. If speed is important, private access offers faster start times, though there is a cost involved.
What's the difference between Mounjaro, Wegovy, and Saxenda?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist, once weekly. Wegovy (semaglutide) is a GLP-1 agonist, once weekly. Saxenda (liraglutide) is a GLP-1 agonist, once daily. All three support weight management through appetite regulation. Mounjaro and Wegovy have stronger trial data for weight loss. Your prescriber will recommend the most suitable option based on your health profile.
Should I try diet and exercise alone before seeking prescription medication?
Many people try lifestyle changes first, and this is often recommended as a starting point. However, if you have tried diet and exercise without adequate results, or have a BMI over 30 with health complications, prescription medication may be appropriate. Your GP can help you decide. Our GLP-1 weight loss calculator can help you explore potential outcomes with medication to inform your conversation with your healthcare provider.
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.