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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Prescription Medications for Weight Loss in the UK
If you're struggling with your weight, prescription medications may be an option worth discussing with your GP. The UK has several evidence-based weight loss medications available, though access varies depending on whether you use the NHS or private prescribing. Understanding what's available, who qualifies, and how these medications work can help you make an informed decision about your weight management journey. This guide covers the prescription weight loss options currently licensed in the UK and how to explore whether they might be suitable for you.
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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
Three prescription medications are currently licensed in the UK specifically 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 work as GLP-1 receptor agonists (Mounjaro is a dual GIP/GLP-1 agonist), which means they help regulate appetite and support feeling fuller after meals.
In clinical trials, these medications showed meaningful results when combined with diet and exercise. For example, Mounjaro users lost an average of 15–21% of their body weight over 72 weeks, whilst Wegovy users lost approximately 15% at the maximum dose. However, individual results vary significantly — some people respond better than others. These are prescription-only medicines and require a clinical assessment before being prescribed.
- Mounjaro: 2.5 mg to 15 mg once weekly
- Wegovy: 0.25 mg to 2.4 mg once weekly
- Saxenda: 0.6 mg to 3 mg once daily
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 Prescribing
In the UK, prescription weight loss medications are available through both NHS specialist services and private online prescribing. NHS access typically requires a referral to a tier 3 specialist weight management service from your GP — though waiting times can be several months to over a year in many areas, and availability varies significantly by region. Private access is faster: you complete an online consultation with a UK-licensed prescriber, and if approved, the prescription is dispensed by a registered pharmacy.
Regardless of route, you'll need a BMI of 30 or above, or 27–29.9 with a weight-related health condition (such as type 2 diabetes, high blood pressure, or sleep apnoea). Lower BMI thresholds apply for people of South Asian, Chinese, Black African, or Black Caribbean heritage. The best first step is to discuss weight management options with your GP, who can assess your individual situation and refer you appropriately.
To understand whether these medications might be suitable for you, start by checking your BMI using our free BMI calculator — this will help you see where you currently stand against NHS guidelines. Eligibility depends on your BMI, any existing health conditions, and medical history. Your GP or a licensed prescriber will assess the full picture before recommending treatment. It's important to remember that weight loss medications work best alongside a reduced-calorie diet and regular physical activity — they're a tool to support lifestyle changes, not a replacement for them. You can track your progress with our free progress tracker if you begin treatment, which helps you see results over time.
- 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's the difference between Mounjaro and Wegovy?
Both are once-weekly injections licensed for weight loss in the UK. Mounjaro (tirzepatide) is a dual GIP/GLP-1 agonist, whilst Wegovy (semaglutide) is a GLP-1 agonist only. Clinical trials show similar average weight loss (~15–21%), but they work slightly differently. Your prescriber will advise which is more suitable based on your health profile.
Can I get weight loss medication on the NHS?
Yes, but access is through specialist tier 3 weight management services, usually via GP referral. Availability and waiting times vary significantly by region. You'll need a BMI of 30+ or 27–29.9 with weight-related health conditions. Check with your local integrated care board (ICB) about availability in your area.
What are the common side effects of weight loss injections?
Nausea, diarrhoea, constipation, and stomach discomfort are the most common side effects, especially when starting or increasing doses. Most side effects improve over time. Serious side effects are rare but can include pancreatitis or gallbladder problems. Your prescriber will discuss all risks before treatment begins.
How much weight will I lose with these medications?
Individual results vary significantly. Clinical trials show average weight loss of 15–21% of body weight, but some people lose more, others less. Weight loss depends on the dose, how your body responds, diet, exercise, and other factors. Your prescriber can give you realistic expectations based on your situation.
Do I need to change my diet and exercise if I take weight loss medication?
Yes. These medications work best alongside a reduced-calorie diet and regular physical activity. They're not a standalone solution — they support lifestyle changes by helping reduce appetite and cravings, making it easier to stick to healthier habits. Long-term success requires both medication and behaviour change.
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.