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 Aids in the UK: Prescription Medication Options
If you're exploring weight loss aids in the UK, prescription medication is now available for eligible adults through both NHS and private routes. Weight management in the UK has evolved significantly, with several licensed options designed to support sustainable weight loss alongside lifestyle changes. Understanding what's available, who qualifies, and how to access these treatments is the first step toward finding the right approach for your health goals.
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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 Weight Loss Medications
Three prescription-only medications are currently licensed for weight management in the UK: Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). Mounjaro and Wegovy are injectable pens used once weekly, whilst Saxenda is a daily injection. These are GLP-1 and GIP receptor agonist medications that work by signalling to your brain that you're full, reducing appetite and food cravings. Clinical trials have shown that Mounjaro helps participants lose an average of 15–21% of their body weight, whilst Wegovy supports an average loss of around 15% — though individual results vary significantly. Eligibility for prescription weight loss medication in the UK typically requires:
- A BMI of 30 kg/m² or above, OR
- A BMI of 27–29.9 kg/m² with at least one weight-related health condition (type 2 diabetes, high blood pressure, sleep apnoea, or cardiovascular disease)
- For South Asian, Chinese, Black African, and Black Caribbean adults, lower BMI thresholds may apply due to higher health risks at lower weights
Use our free BMI calculator above to check where you fall within these ranges. Your GP can assess whether you meet the clinical criteria for treatment.
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
NHS access is through specialist tier 3 or 4 weight management services. Your GP can refer you to your local specialist weight management service, though availability and waiting times vary significantly by region. Many areas have substantial waiting lists, sometimes lasting months or years.
Private access is available through GPhC-registered online pharmacies following an online clinical assessment by a UK-licensed prescriber. This route typically offers faster access without NHS waiting lists, though costs vary by dose and provider. Both routes require a clinical assessment to confirm eligibility and suitability. Whichever route you choose, our GLP-1 weight loss calculator can help you understand potential outcomes at different doses, whilst our progress tracker allows you to monitor your journey. Start by speaking with your GP about whether prescription weight loss medication is right for you.
- 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 management in the UK. Mounjaro is a dual GIP and GLP-1 agonist, whilst Wegovy is a GLP-1 agonist only. Clinical data suggests Mounjaro may produce slightly greater average weight loss (15–21% vs 15%), though individual results vary. Your prescriber will assess which is most suitable based on your personal health profile and medical history.
How quickly will I lose weight on prescription weight loss medication?
Weight loss varies significantly between individuals. Clinical trials show average losses over 68–72 weeks, not immediate results. Most people lose weight gradually as their dose is increased over several weeks. The NHS recommends a sustainable rate of 0.5–1 kg per week. These medications work best alongside reduced-calorie diet and increased physical activity — they're a support tool, not a replacement for lifestyle changes.
Can I access weight loss injections on the NHS?
Yes, NICE has approved tirzepatide (Mounjaro) and semaglutide (Wegovy) for use within NHS specialist weight management services. However, access is through tier 3 or 4 specialist services, not standard GP prescription. You'll need a GP referral, and availability varies significantly by region. Private access is also available without NHS referral but involves costs.
What are the common side effects of weight loss medication?
The most common side effects include nausea, diarrhoea, constipation, stomach pain, and indigestion — especially when starting or increasing doses. These typically improve over time as your body adjusts. Serious side effects are rare but can include pancreatitis (severe stomach pain) or gallbladder problems. Always report unexpected symptoms to your prescriber immediately.
Do I need to keep taking weight loss medication indefinitely?
Weight loss medications are typically used for as long as they continue to be effective and beneficial for your health. Some people maintain weight loss after stopping; others regain weight. Your prescriber will discuss the right duration for you based on your individual response, health goals, and any weight-related health conditions. This is a conversation to have regularly with your healthcare team.
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.