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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New Weight Loss Medicine — UK Options Explained
If you're exploring new weight loss medicine options in the UK, you have several prescription medications now available that may support weight management alongside lifestyle changes. Recent advances in weight loss medication have expanded what's available on the NHS and privately, particularly GLP-1 and dual-action receptor agonists. This guide covers the latest weight management medicines licensed in the UK, who's eligible, and how to access them through your GP or private prescriber. Understanding your options is the first step toward making an informed decision about weight loss treatment.
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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 Medicines and How They Work
The most significant development in recent weight loss medicine is the availability of GLP-1 receptor agonist medications and dual GIP/GLP-1 agonists. Currently licensed for weight management in the UK are:
- Mounjaro (tirzepatide) — a dual GIP and GLP-1 receptor agonist, once-weekly injection, doses 2.5mg to 15mg. Clinical trials showed average weight loss of 15–21% of body weight alongside a reduced-calorie diet and increased physical activity.
- Wegovy (semaglutide) — a GLP-1 receptor agonist, once-weekly injection, maximum dose 2.4mg. In clinical trials, average weight loss was approximately 15% of body weight.
- Saxenda (liraglutide) — a GLP-1 receptor agonist, once-daily injection, maximum dose 3mg. Available for several years, established evidence base.
These prescription weight loss medications work by helping regulate appetite, reduce food cravings, and support feeling fuller after smaller meals. Results vary significantly between individuals. All three are prescription-only medicines requiring a clinical assessment before prescribing.
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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
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Eligibility and How to Access Weight Loss Medicine in the UK
To be eligible for prescription weight loss medicine 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 cardiovascular disease. For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds apply due to higher health risks at lower weights.
You can access prescription weight loss medication through two routes: The NHS specialist weight management services (tier 3), which requires a GP referral and may involve waiting lists, or private prescribing through UK-licensed online services following a clinical assessment. Your GP can discuss which option suits your circumstances and health profile. Use our free BMI calculator to check your starting point, then have a conversation with your healthcare provider about eligibility and suitability.
- 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 prescription weight loss injections, but Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist while Wegovy (semaglutide) is a GLP-1 agonist only. Mounjaro requires doses of 2.5mg to 15mg once weekly; Wegovy goes up to 2.4mg once weekly. Clinical trials suggest Mounjaro may produce slightly higher average weight loss, but individual results vary significantly. A prescriber will assess which is appropriate for you.
Can I get prescription weight loss medicine on the NHS?
Yes. NHS specialist weight management services (tier 3) can prescribe Mounjaro, Wegovy, and Saxenda. Access requires a GP referral and availability varies significantly by region. Waiting lists can be substantial in some areas. You can also access these medications privately through GPhC-registered online prescribers without an NHS referral, though you'll pay privately.
What are the common side effects of new weight loss medicines?
The most common side effects of GLP-1 and GIP/GLP-1 medications include nausea, diarrhoea, vomiting, constipation, and stomach pain. These typically improve as your body adjusts. Serious side effects are rare but can include severe stomach pain (possible pancreatitis) or serious allergic reactions. Always report any concerning symptoms to your prescriber immediately.
How much weight will I lose with these medicines?
Clinical trials show average weight loss of 15–21% of body weight, but individual results vary considerably. Some people lose less, some lose more. Weight loss depends on the dose, your individual response, adherence, and lifestyle changes. A prescriber will discuss realistic expectations for your situation. Our GLP-1 weight loss calculator can help estimate potential outcomes at different doses.
Do I need to change my diet and exercise if I take weight loss medicine?
Yes. Prescription weight loss medicines work best alongside a reduced-calorie diet and increased physical activity. These medications support weight loss but don't replace healthy lifestyle changes. Your GP or prescriber will discuss dietary and exercise recommendations as part of your overall weight management plan.
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.