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 Jabs — What You Need to Know
Weight loss jabs, also known as slimming injections or weight management jabs, are prescription-only medicines that may help support weight loss when used alongside a reduced-calorie diet and increased physical activity. In the UK, three GLP-1 and GIP receptor agonist medications are currently licensed for weight management: Mounjaro, Wegovy, and Saxenda. These are genuine prescription medications available through both NHS specialist services and private prescribing pathways. This guide explains how they work, who may be eligible, and how to access them in the UK.
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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 Jabs and Eligibility
Three prescription weight loss jabs are available in the UK for weight management:
- Mounjaro (tirzepatide) — a dual GIP and GLP-1 receptor agonist, once-weekly injection, doses 2.5 mg to 15 mg
- Wegovy (semaglutide) — a GLP-1 receptor agonist, once-weekly injection, doses 0.25 mg to 2.4 mg
- Saxenda (liraglutide) — a GLP-1 receptor agonist, once-daily injection
All three are prescription-only and require a clinical assessment before prescribing. You may be eligible for prescription weight loss medication if you have a BMI of 30 kg/m² or above, or a BMI of 27 to 29.9 kg/m² with at least one weight-related health condition (type 2 diabetes, prediabetes, high blood pressure, high cholesterol, sleep apnoea, or cardiovascular disease). If you are of South Asian, Chinese, Black African, or Black Caribbean descent, you may be eligible at a lower BMI. Use our free BMI calculator above to check where you stand, and speak to your GP about whether prescription weight loss medication might be appropriate for you.
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 vs Private Access in the UK
NHS access: Weight loss jabs are available through NHS specialist tier 3 and tier 4 weight management services. This typically requires a referral from your GP, and availability varies significantly by region and local NHS commissioning. Waiting lists can be several months or longer in many areas.
Private access: Weight loss jabs are available through private online prescribing services following a clinical assessment with a UK-licensed prescriber. This route does not require an NHS referral and can be faster, though there is a cost. Both pathways require a prescription from a qualified healthcare professional — weight loss jabs are never available without clinical assessment. Our GLP-1 weight loss calculator can help you understand potential outcomes if you are considering treatment.
To find out if you are eligible, start by speaking to your GP. They can assess your individual health profile, discuss whether prescription weight loss medication is suitable, and explain local NHS options if available. If you prefer private access, several GPhC-registered online services offer remote consultations with UK prescribers. Weight loss medication works best alongside lifestyle changes — reduced calorie intake, regular physical activity, and behaviour change support. Track your progress with our free progress tracker as you work towards your weight loss goals.
- 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.
Are weight loss jabs safe?
Weight loss jabs like Mounjaro and Wegovy are prescription-only medicines that have undergone rigorous clinical testing and regulatory approval by the MHRA. Common side effects include nausea and diarrhoea, usually temporary. Serious side effects are rare but possible. Your GP or prescriber will assess your individual health and discuss risks and benefits before prescribing. Always report any concerning symptoms.
How much weight can I expect to lose with weight loss jabs?
Clinical trials show that people using Mounjaro lost an average of 15–21% of their body weight, while Wegovy users lost around 15% on average — but individual results vary significantly. Weight loss depends on the dose, your adherence, diet, exercise, and individual metabolism. These medications work best alongside reduced-calorie diet and increased physical activity, not instead of lifestyle changes.
What's the difference between Mounjaro and Wegovy?
Both are once-weekly prescription injections for weight management, but they work slightly differently. Mounjaro is a dual GIP and GLP-1 receptor agonist, while Wegovy is a GLP-1 receptor agonist only. In clinical trials, Mounjaro showed slightly higher average weight loss, but both are effective. Your GP or prescriber can discuss which might be better suited to your individual circumstances.
Can I get weight loss jabs on the NHS?
Yes, weight loss jabs are available on the NHS through specialist tier 3 and tier 4 weight management services. However, availability varies significantly by region and waiting lists can be long. Start by speaking to your GP about referral options. Private access is also available through online prescribing services if you prefer a faster route, though there is a cost involved.
Do I need to change my diet if I use weight loss jabs?
Yes. Weight loss medications like Mounjaro and Wegovy work best alongside a reduced-calorie diet and increased physical activity. The medication helps reduce appetite and cravings, but it is not a replacement for lifestyle change. Your prescriber should discuss diet and exercise expectations as part of your treatment plan. Use our BMI calculator and progress tracker to monitor your health metrics alongside medication use.
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.