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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12 Kg Weight Loss: UK Prescription Medication Guide
Losing 12 kg is a significant health goal that, for many people in the UK, can be supported by prescription weight management medication alongside diet and exercise. If you're considering professional help to lose weight, understanding the prescription options available—and whether you're eligible—is an important first step. This guide explains the UK-licensed medications, how they work, and how to find out if you might qualify for treatment through the NHS or private prescribing.
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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: What's Available?
Three prescription medications are currently licensed in the UK for weight management: Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). All three are GLP-1 or dual GIP/GLP-1 receptor agonists that may help reduce appetite and support feeling fuller after smaller meals.
Mounjaro is a once-weekly injection with a dual mechanism, helping to regulate both appetite and fat utilisation. In clinical trials, participants lost an average of 15–21% of their body weight at the highest dose—though individual results vary significantly. Wegovy is also a once-weekly injection and showed average weight loss of around 15% in clinical trials. Saxenda is a daily injection option with slightly lower average weight loss results.
For a 12 kg weight loss goal, this represents approximately 15–20% of body weight for most adults, which aligns with the typical range seen in clinical trials. However, achieving this requires combining medication with a reduced-calorie diet and increased physical activity. A prescriber will assess which medication, if any, is suitable for you based on your individual health profile.
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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
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
NHS vs Private: How to Access Weight Loss Medication in the UK
NHS access: Prescription weight loss medications are available through specialist tier 3 and tier 4 weight management services, typically following a referral from your GP. However, NHS availability varies significantly by region, and waiting lists can be lengthy in many areas—sometimes several months or longer.
Private access: GPhC-registered online pharmacies offer prescription weight loss medications following an online clinical assessment with a UK-licensed prescriber. This route is faster and doesn't require an NHS referral. Costs typically range from £129–£320 per month depending on the dose and provider.
Whether you pursue NHS or private treatment, the process is the same: a prescriber assesses your BMI, health history, and weight-related conditions to determine eligibility. Start by speaking with your GP about your weight loss goals—they can advise on local NHS options or discuss private alternatives.
- 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.
Who is eligible for prescription weight loss medication in the UK?
Adults with a BMI of 30 or above, or a BMI of 27–29.9 with weight-related health conditions (such as type 2 diabetes, high blood pressure, or cardiovascular disease) may be eligible. For people of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds may apply. A prescriber or your GP will assess your individual eligibility.
How much weight can I expect to lose with Mounjaro or Wegovy?
Clinical trials showed average weight loss of around 15–21% of body weight with Mounjaro and approximately 15% with Wegovy, achieved alongside a reduced-calorie diet and exercise. However, individual results vary significantly—some people lose more, others less. Use our free GLP-1 weight loss calculator to estimate potential outcomes based on your starting weight and chosen dose.
Is 12 kg weight loss realistic with prescription medication?
Yes, 12 kg represents approximately 15–20% of body weight for most adults, which falls within the typical range achieved in clinical trials when combined with diet and exercise. However, results depend on your starting weight, adherence to medication, and lifestyle changes. Your prescriber can discuss realistic timelines for your specific situation.
Can I get weight loss injections on the NHS?
Prescription weight loss medications including Mounjaro and Wegovy are available on the NHS through specialist weight management services. Access varies by region and typically requires a GP referral. Waiting lists can be long, so ask your GP about local availability in your area.
How do I start: NHS or private?
If you'd like to explore NHS options, speak with your GP about referral to your local tier 3 weight management service. For faster private access, you can use an online GPhC-registered pharmacy after a clinical assessment. Either route requires a prescription from a licensed UK prescriber and a medical assessment of your eligibility.
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.