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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Prescribed Weight Loss Medication in the UK
If you're struggling with your weight and looking for medical support, prescribed weight loss medication may be an option worth discussing with your GP. The UK now has several prescription medications licensed specifically for weight management, available both through the NHS and privately. These are evidence-based treatments designed to work alongside dietary changes and increased physical activity, not as a standalone solution. Understanding what's available, who is eligible, and how to access these treatments is an important first step on your weight management journey.
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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.
UK-Licensed Weight Loss Medications and Eligibility
Three main prescription medications are currently licensed in the UK for weight management: Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). Mounjaro and Wegovy are once-weekly injections, whilst Saxenda requires a daily injection. All three work by activating hormone pathways that help reduce appetite and support feeling fuller after smaller meals.
To be eligible for prescribed weight loss medication in the UK, you typically need a BMI of 30 or above, or a BMI of 27–29.9 with at least one weight-related health condition such as type 2 diabetes, high blood pressure, or heart disease. Adults of South Asian, Chinese, Black African, or Black Caribbean heritage may have lower BMI thresholds due to higher health risks at these levels.
Clinical trial evidence shows these medications can help people lose an average of 15–21% of their body weight when combined with a reduced-calorie diet and increased physical activity, though individual results vary significantly. Check your personal BMI using our free BMI calculator above to see whether you might be in an eligible range.
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.
Accessing Weight Loss Medication: NHS vs Private Routes
In the UK, you can access prescribed weight loss medication through two main routes. NHS access is through specialist tier 3 weight management services, usually following a GP referral. However, NHS availability varies by region and waiting lists can be lengthy in some areas. Private access is available through GPhC-registered online pharmacies and prescribers, allowing you to access medication without waiting for NHS specialist referral.
The first step is always to speak with your GP about whether weight management medication might be suitable for you. Your GP can discuss your medical history, current health conditions, and whether you meet eligibility criteria. If NHS specialist services are available in your area, your GP can make a referral. Alternatively, you can pursue a private online clinical assessment with a UK-licensed prescriber. Either route requires a proper medical evaluation before any medication is prescribed. Use our free weight loss calculator to project potential outcomes at different doses.
- 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 you lose with prescribed weight loss medication?
Clinical trials show an average loss of 15–21% of body weight over approximately 68–72 weeks, alongside reduced-calorie diet and increased physical activity. Individual results vary significantly — some people lose more, some less. Results also depend on which medication you take, the dose you reach, and how consistently you follow lifestyle changes alongside medication.
Is prescribed weight loss medication available on the NHS?
Yes, tirzepatide (Mounjaro) and semaglutide (Wegovy) are both NICE-approved for use on the NHS through specialist weight management services. However, access varies by region and waiting times can be several months to over a year. Your GP can refer you to local tier 3 services if available.
Can I get weight loss medication online in the UK?
Yes, private online prescribing is available through GPhC-registered pharmacies. You complete an online clinical assessment with a UK-licensed prescriber who will assess your eligibility based on your BMI, health conditions, and medical history. If approved, your prescription is dispensed and delivered.
What are the side effects of weight loss injections?
Common side effects include nausea, diarrhoea, vomiting, constipation, and stomach pain, particularly during dose increases. These typically improve over time. Less common side effects include headache, fatigue, and injection site reactions. Serious side effects are rare but can include severe stomach pain (pancreatitis) or gallbladder problems.
What is the difference between Mounjaro and Wegovy for weight loss?
Both are once-weekly injections, but Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist, whilst Wegovy (semaglutide) is a GLP-1 agonist only. Clinical trials suggest Mounjaro may produce slightly higher average weight loss (up to 21% vs 15%), but individual results vary. Your prescriber will advise which is more appropriate based on your 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.