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
Weight Loss Jabs: What You Need to Know
Weight loss jabs—also called slimming injections or GLP-1 injections—are prescription-only medicines that may help support weight management in UK adults. These injectable medications work by mimicking natural hormones that regulate appetite and help you feel fuller for longer. They're used alongside a reduced-calorie diet and increased physical activity. This guide explains how they work, who may be eligible, and how to access them through the NHS or privately in the UK.
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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.
How Weight Loss Jabs Work
Weight loss jabs contain active ingredients called GLP-1 receptor agonists or GIP/GLP-1 receptor agonists. These mimic natural hormones your gut produces after eating.
GLP-1 medications (like Wegovy, the semaglutide injection) work by:
- Signalling to your brain that you're full, reducing appetite
- Helping you feel satisfied after smaller meals
- Slowing how quickly food leaves your stomach
- Supporting better blood sugar control
The dual GIP/GLP-1 medication (Mounjaro, tirzepatide) activates two hormone pathways, which may provide stronger appetite regulation. In clinical trials, weight loss jabs helped participants lose an average of 15–21% of their body weight, though individual results vary significantly. These injections are prescription-only and require clinical assessment to confirm suitability.
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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.
Eligibility and Access in the UK
You may be eligible for prescription weight loss medication if you have a BMI of 30 or above, or 27 or above with a weight-related health condition (such as type 2 diabetes, high blood pressure, or heart disease). For people of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds may apply.
NHS access: Through specialist tier 3 weight management services via GP referral. Availability and waiting times vary by region. Private access: Through online consultations with UK-licensed prescribers, dispensed by registered pharmacies. Try our GLP-1 weight loss calculator to explore potential outcomes at different doses, and use our BMI calculator to check your current category.
Cost and types: Private costs range from approximately £129–£320 monthly depending on dose. UK-licensed weight loss injections include Wegovy (semaglutide, once weekly), Mounjaro (tirzepatide, once weekly), and Saxenda (liraglutide, daily). All are prescription-only and require a consultation to assess medical history, current medications, and contraindications. Weight loss jabs work best alongside lifestyle changes—diet and physical activity remain essential for sustainable weight loss.
- 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?
Prescription weight loss medications are licensed and monitored by the MHRA. Common side effects include nausea and stomach upset, usually mild and temporary. Serious side effects are rare but require immediate medical attention (e.g. severe abdominal pain). A prescriber assesses your individual health before prescribing to ensure safety.
How much weight will I lose with weight loss jabs?
In clinical trials, people lost an average of 15–21% of body weight over 68–72 weeks alongside diet and exercise. Individual results vary significantly depending on starting weight, adherence, diet, and activity level. Weight loss is not assured. A prescriber discusses realistic expectations during consultation.
Can I get weight loss jabs on the NHS in the UK?
Yes, but access is through specialist tier 3 weight management services. You'll need a GP referral. Availability varies by region (ICB), and waiting lists can be lengthy. Private online prescribing is an alternative if NHS waiting times are long.
What's the difference between Wegovy and Ozempic?
Both contain semaglutide but serve different purposes. Wegovy is licensed for weight management (up to 2.4 mg weekly). Ozempic is licensed for type 2 diabetes (up to 2 mg). Ozempic is not approved for weight loss in the UK—using it off-label is not recommended. Always use the licensed medication for your specific condition.
Do I need to stay on weight loss jabs forever?
No prescribed duration is set. Your prescriber reviews whether to continue based on your progress and health. Some people maintain results after stopping if lifestyle changes stick; others regain weight. It's a tool to support behaviour change, not a permanent solution on its own.
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.