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 at Pharmacies: What You Need to Know
Weight loss jabs (often called "slimming injections" or "fat jabs") are prescription-only GLP-1 receptor agonist medications available through UK pharmacies following a clinical assessment. These injectable medications have gained significant attention as a weight management option for UK adults. This guide explains how they work, who is eligible, and what to expect if you're considering this form of prescription weight loss medication. Always consult your GP or a licensed prescriber to determine if weight loss jabs are appropriate for your individual circumstances.
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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.
How Weight Loss Jabs Work and What They Are
Weight loss jabs are injectable medications that activate GLP-1 (glucagon-like peptide-1) or dual GIP/GLP-1 hormone pathways in your body. These hormones are naturally produced in your gut after eating and signal to your brain that you're full. Weight loss medications amplify these signals, which may help reduce appetite, decrease food cravings, and support feeling fuller after smaller meals.
- Wegovy (semaglutide) — once-weekly GLP-1 injection, doses up to 2.4 mg, average weight loss around 15% body weight in clinical trials
- Mounjaro (tirzepatide) — once-weekly dual GIP and GLP-1 injection, doses up to 15 mg, average weight loss around 15–21% body weight
- Saxenda (liraglutide) — daily GLP-1 injection, older option, less commonly prescribed now
These medications are prescription-only and not cosmetic injections. They require a clinical assessment by a UK-licensed prescriber and work alongside reduced-calorie diet and increased physical activity — 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.
UK Eligibility and How to Access Weight Loss Jabs
In the UK, you may be eligible for prescription weight loss jabs if you have a BMI of 30 kg/m² or above, or 27–29.9 with at least one weight-related health condition (such as type 2 diabetes, prediabetes, high blood pressure, or sleep apnoea). Lower thresholds apply for adults of South Asian, Chinese, Black African, or Black Caribbean heritage — eligibility may start at BMI 27.5 or above.
Weight loss jabs are available through two routes: NHS specialist weight management services (via GP referral, though availability and waiting lists vary significantly by region) or private online prescribing with a GPhC-registered pharmacy. Try our free GLP-1 weight loss calculator to explore potential results at different doses, and use our BMI calculator to check your starting point.
Private access via pharmacies: Online consultation with a UK-licensed prescriber, prescription issued if clinically suitable, dispensed by GPhC-registered pharmacy, typically costs £129–£320/month depending on dose. NHS access: Referral to tier 3 specialist weight management service, variable availability and waiting times, free on NHS if approved. Both routes require a clinical assessment — you cannot buy weight loss jabs without a valid prescription.
- 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 assured to work?
No. Weight loss jabs may help some people lose weight, but individual results vary significantly. Clinical trials showed average weight losses of around 15–21%, but some people lose less and some more. Results depend on genetics, adherence to the medication schedule, diet, and physical activity. Your prescriber can discuss realistic expectations for your situation.
What are the side effects of weight loss jabs?
Very common side effects include nausea, diarrhoea, vomiting, and constipation — usually most intense in the first few weeks and often improve over time. Common side effects include indigestion, headache, fatigue, and injection site reactions. Serious side effects are rare but include severe stomach pain (possible pancreatitis) and gallbladder problems. Always report persistent or concerning symptoms to your prescriber.
Can I get weight loss jabs on the NHS?
Yes, but access varies significantly by region. You need a referral from your GP to a tier 3 specialist weight management service. Waiting lists can be very long in some areas (months to years). Private online prescribing offers faster access without NHS referral if you have a valid prescription from a licensed UK prescriber. Check your local ICB (integrated care board) website for NHS availability in your area.
How long do I need to take weight loss jabs?
Duration varies by individual and prescriber guidance. Some people take them for several months to lose weight then transition to maintenance, while others continue longer-term. Stopping the medication usually means weight may return gradually. Your prescriber will advise on the best approach for your health goals and circumstances. Weight management often requires ongoing support and lifestyle changes.
Do weight loss jabs interact with other medications?
Yes, some interactions are possible. Weight loss injections may reduce the absorption of oral contraceptives — women on the pill should use additional contraception for 4 weeks after starting and after dose increases. If you take diabetes medications like insulin or sulphonylureas, doses may need adjusting. Always tell your prescriber about all medications and supplements you take.
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.