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 Transformation: UK Prescription Medication Options
A weight loss transformation is achievable with the right support — and for many UK adults, prescription medication can be part of that journey. If you've tried lifestyle changes alone and are struggling to lose weight, you may be eligible for prescription weight management treatment through the NHS or private prescribing. Understanding your options, how to access them, and what results to expect is the first step toward meaningful change. This guide covers UK-licensed medications, eligibility criteria, and how to start a conversation with your GP about whether prescription weight loss treatment 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-Licensed Prescription Weight Loss Medications
Three 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, while Saxenda is a daily injection. All three are GLP-1 receptor agonists (Mounjaro is dual GIP and GLP-1), which work by helping regulate appetite and supporting you to feel fuller after smaller meals. Clinical trials have shown that these medications, used alongside a reduced-calorie diet and increased physical activity, can support significant weight loss. On average, Mounjaro users lost 15–21% of their body weight, while Wegovy users lost approximately 15% in clinical trials — though individual results vary considerably. These are prescription-only medications requiring a clinical assessment before being prescribed. Eligibility typically includes adults with a BMI of 30 or above, or 27 or above with weight-related health conditions such as type 2 diabetes, high blood pressure, or sleep apnoea. For people of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds may apply due to higher health risks at lower weights. Use our free GLP-1 weight loss calculator to explore potential outcomes at different doses, and our BMI calculator to check your current BMI 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
In the UK, prescription weight loss medication is available through two routes: NHS specialist weight management services and private online prescribing. NHS access involves referral from your GP to a tier 3 or 4 specialist weight management service — eligibility and waiting times vary significantly by region. Some areas have very long waiting lists; others have limited capacity. Private access is available through GPhC-registered online prescribing services following a clinical consultation with a UK-licensed prescriber, without requiring NHS referral. The first step is always to speak with your GP about your weight loss goals and whether prescription medication might help. Your GP can assess your individual health, discuss the options available to you locally, and refer you to specialist services if appropriate. They can also advise whether private prescribing might be suitable for your situation. A healthcare professional will review your medical history, current medications, and eligibility before any prescription is issued.
- 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.
What is the difference between Mounjaro and Wegovy?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two hormone pathways, while Wegovy (semaglutide) is a single GLP-1 agonist. Clinical trial data suggests Mounjaro may support slightly higher average weight loss (15–21% vs approximately 15% for Wegovy), though results vary individually. Both are once-weekly injections. The choice between them depends on individual health factors and prescriber recommendation.
Am I eligible for prescription weight loss medication on the NHS?
NHS eligibility typically includes adults with a BMI of 30 or above, or 27–29.9 with weight-related health conditions like type 2 diabetes, high blood pressure, or sleep apnoea. For South Asian, Chinese, Black African, or Black Caribbean adults, thresholds may be lower (BMI 27.5 or above). Speak with your GP to discuss your individual eligibility and local availability.
How much weight can I expect to lose with prescription medication?
Clinical trials show average weight loss of 15–21% of body weight with these medications, used alongside dietary changes and physical activity. However, individual results vary significantly — some people lose more, others less. Our GLP-1 weight loss calculator can help you estimate potential outcomes. Weight loss medications work best combined with lifestyle changes, not as a replacement for them.
What are the most common side effects of weight loss injections?
The most common side effects include nausea, diarrhoea, vomiting, constipation, and stomach pain — especially when starting or increasing doses. These often improve over time as your body adjusts. Serious side effects are rare but include severe stomach pain (possible pancreatitis) and gallbladder problems. Always inform your prescriber of any side effects; they can adjust your dose or discuss alternatives.
How long do I need to take weight loss medication?
Duration depends on your individual circumstances and how well the medication works for you. Some people use it short-term to kickstart weight loss and establish new habits; others use it longer-term for ongoing management. Your prescriber will discuss your goals and monitor your progress regularly. Stopping the medication should be discussed with your prescriber — weight can return if lifestyle changes aren't maintained.
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.