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
Free tracker included with every download this week
Prescription Weight Loss Injections in the UK
Prescription weight loss injections are licensed medications that may help adults lose weight when combined with diet and physical activity. In the UK, three main options are available: Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). These work by affecting appetite hormones and are prescribed only after clinical assessment. Access is available through both NHS specialist services and private prescribing. This guide covers eligibility, how these medications work, and what to expect.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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 Injections and How They Work
Three prescription weight loss injections are currently licensed in the UK:
- Mounjaro (tirzepatide) — A once-weekly injection that activates two hormone pathways (GIP and GLP-1). Clinical trials showed participants lost an average of 15–21% of their body weight over 72 weeks, though individual results vary significantly.
- Wegovy (semaglutide) — A once-weekly GLP-1 injection. In clinical trials, the average weight loss at the maximum dose was approximately 15% of body weight alongside reduced-calorie diet and increased physical activity.
- Saxenda (liraglutide) — A daily injection (different from the once-weekly options). Average weight loss is typically 5–10% of body weight.
All three are GLP-1 or dual GLP-1/GIP medications that help reduce appetite, support feeling fuller after smaller meals, and may slow how quickly food leaves the stomach. Results vary between individuals, and these medications work best alongside lifestyle changes, not instead of them.
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.
Eligibility and How to Access in the UK
You may be eligible for prescription weight loss medication if you have a BMI of 30 or above, or BMI of 27–29.9 with a weight-related health condition such as type 2 diabetes, prediabetes, high blood pressure, or sleep apnoea. Lower BMI thresholds (27.5+) apply if you are of South Asian, Chinese, Black African, or Black Caribbean heritage due to higher health risks at lower weights.
Access is available through NHS specialist tier 3 weight management services (via GP referral) or private prescribing following an online clinical assessment. NHS availability and waiting times vary significantly by region. Your GP can assess your eligibility and discuss which option suits you best. Use our free BMI calculator above to check your current BMI and determine if you may qualify.
- 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) activates two hormone pathways (GIP and GLP-1), whilst Wegovy (semaglutide) activates one (GLP-1 only). Both are once-weekly injections. Clinical trials showed Mounjaro produced slightly higher average weight loss (~21% vs ~15%), but individual results vary. Your GP or prescriber will advise which is most suitable for you.
How much weight can I expect to lose with prescription weight loss injections?
Clinical trials show average weight loss of 5–21% of body weight depending on the medication and dose, achieved alongside diet and exercise changes. However, individual results vary significantly — some people lose more, some less. Weight loss is not assured, and these medications work best as part of a comprehensive lifestyle approach.
Can I get prescription weight loss injections on the NHS?
Yes, but access is through specialist tier 3 weight management services, typically requiring a GP referral. Availability and waiting times vary by region and local NHS commissioning. Private access is also available through GPhC-registered online prescribers following a clinical assessment, though this involves a cost.
Are prescription weight loss injections safe?
These medications are licensed in the UK and have been through rigorous clinical trials. However, they do have side effects — commonly nausea, diarrhoea, and constipation, particularly when starting or increasing doses. Serious side effects are rare but include pancreatitis symptoms and gallbladder issues. Your prescriber will assess whether the medication is safe for you individually.
Do I need to change my diet and exercise when taking prescription weight loss medication?
Yes. Clinical trials showed weight loss only when medication was combined with a reduced-calorie diet and increased physical activity. These medications support appetite reduction and may make lifestyle changes easier, but they work best alongside behavioural changes, not instead of them. Try our GLP-1 weight loss calculator to see projected outcomes with different doses.
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.