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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Five Week Weight Loss with Prescription Medication in the UK
Losing weight in five weeks requires a structured approach, and for many UK adults, prescription medication combined with lifestyle changes can be part of an effective strategy. The most evidence-based prescription options available on the NHS and privately are GLP-1 receptor agonist medications like Mounjaro and Wegovy. These work alongside a reduced-calorie diet and increased physical activity. This guide explains what's available, who's eligible, and how to find out if prescription weight loss medication is right for you.
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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 Prescription Weight Loss Options and How They Work
Three main prescription weight management medications are licensed in the UK: Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). Mounjaro and Wegovy are once-weekly injections; Saxenda is a daily injection. In clinical trials, these medications helped participants lose an average of 15–21% of body weight over several months, though individual results vary significantly.
All three are GLP-1 receptor agonists (or in Mounjaro's case, a dual GIP/GLP-1 agonist) that work by reducing appetite, increasing fullness after meals, and slowing how quickly food leaves the stomach. These medicines are prescription-only and require a clinical assessment to determine eligibility. Weight loss with these medications typically becomes noticeable after 4–6 weeks, making the five-week timeline realistic for seeing initial changes, though most significant loss occurs over months.
- Mounjaro: Dual mechanism, doses 2.5–15 mg weekly
- Wegovy: GLP-1 agonist, doses 0.25–2.4 mg weekly
- Saxenda: GLP-1 agonist, daily injections up to 3 mg
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 and How to Find Out If You're Eligible
In the UK, prescription weight loss medication is available through two routes: NHS specialist weight management services or private prescribing through licensed online providers. NHS access requires referral from your GP to a tier 3 specialist service—availability varies significantly by region, and waiting lists can be substantial. Private access is available immediately through a GPhC-registered pharmacy following an online clinical assessment with a UK-licensed prescriber.
You may be eligible if you have a BMI of 30 or above, or a BMI of 27–29.9 with a weight-related health condition such as type 2 diabetes, high blood pressure, or heart disease. Use our free BMI calculator above to check your current BMI. Your first step is to speak with your GP about whether prescription weight loss medication is appropriate for you. They can discuss your options, assess your medical history, and refer you to specialist services if suitable.
Realistic expectations for five weeks: with prescription medication and a reduced-calorie diet, you might expect to lose 2–4 kg (4–9 lbs), though this varies based on your starting weight, adherence, and individual metabolism. The NHS recommends a safe loss rate of 0.5–1 kg per week. Weight management medications work best as part of a comprehensive approach including dietary changes and increased physical activity—they are not a substitute for lifestyle modifications. Track your progress using our free progress tracker to monitor changes week by week and stay motivated.
- 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.
How much weight can I realistically lose in five weeks with prescription medication?
In five weeks with GLP-1 medication, diet changes, and exercise, most people lose 2–4 kg (4–9 lbs). Individual results vary widely based on starting weight, medication dose, calorie intake, and activity level. The NHS recommends a sustainable loss rate of 0.5–1 kg per week. Medication effects also take time to build—most notice appetite changes after 2–3 weeks.
Can I get prescription weight loss medication on the NHS?
Yes. NICE has approved tirzepatide (Mounjaro) and semaglutide (Wegovy) for NHS use through specialist tier 3 weight management services. You'll need a GP referral. Availability varies significantly by region and waiting lists can be long. Private options are available immediately through licensed online providers if you prefer not to wait.
What's the difference between Mounjaro and Wegovy?
Mounjaro (tirzepatide) is a dual GIP/GLP-1 receptor agonist, while Wegovy (semaglutide) is a GLP-1 agonist only. Clinical trials suggest Mounjaro may produce slightly greater average weight loss (15–21% vs ~15%), but results vary individually. Both require weekly injections and clinical assessment. Your prescriber will advise which is more suitable for you.
What are the common side effects of GLP-1 weight loss injections?
Very common side effects include nausea, diarrhoea, vomiting, constipation, and stomach pain. These typically ease as your body adjusts, often within 2–4 weeks. Less common effects include headache, fatigue, and injection site reactions. Serious side effects are rare but include severe abdominal pain (possible pancreatitis) and gallbladder problems—seek medical attention immediately if these occur.
How do I find out if I'm eligible for prescription weight loss medication?
Start by speaking with your GP. You're likely eligible if your BMI is 30 or above, or 27–29.9 with a weight-related health condition such as diabetes or high blood pressure. Check your BMI using our free calculator. Your GP can refer you to NHS specialist services or discuss private options. A licensed prescriber will then assess your suitability based on your full medical history.
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.