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
What Are Diet Jabs? Your UK Health Guide
Diet jabs are prescription-only weight loss injections containing GLP-1 receptor agonist medications, licensed in the UK for weight management in adults. Commonly called "slimming jabs" or "weight loss injections", they work by mimicking a natural hormone that helps regulate appetite and blood sugar. The most widely available options in the UK are Wegovy (semaglutide) and Mounjaro (tirzepatide). Access is available through NHS specialist weight management services or private prescribing following a clinical assessment. Individual results vary, and these medications work alongside dietary changes and increased physical activity, not instead of them.
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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 GLP-1 Diet Jabs Work
Diet jabs contain GLP-1 receptor agonist medications that activate a natural hormone pathway in your body. GLP-1 (glucagon-like peptide-1) is produced in your gut after eating and signals your brain that you're full, helping you feel satisfied with smaller meals.
- Reduces appetite: Helps you feel fuller faster and reduces food cravings
- Slows digestion: Food moves through your stomach more slowly, extending feelings of fullness
- Supports blood sugar: Helps regulate blood glucose levels naturally
- Once weekly: Both Wegovy and Mounjaro are injected once a week
Clinical trials showed that people using these medications alongside a reduced-calorie diet and increased physical activity achieved significant weight loss. In STEP trials, Wegovy users lost an average of approximately 15% of their body weight over 68 weeks. However, results vary between individuals, and medication must be combined with lifestyle changes for best outcomes.
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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.
Accessing Diet Jabs in the UK
There are two main routes to access diet jabs in the UK: NHS specialist services and private online prescribing.
- NHS route: Ask your GP for a referral to a tier 3 specialist weight management service. Availability varies by region, and waiting times can be lengthy in many areas
- Private route: Use a GPhC-registered online pharmacy to book an online consultation with a UK-licensed prescriber. If deemed clinically appropriate, a prescription is issued and medication dispensed by post
- Eligibility: Generally available for adults with a BMI of 30 or above, or BMI 27–29.9 with weight-related health conditions (type 2 diabetes, high blood pressure, sleep apnoea, or cardiovascular disease)
- Assessment required: All prescriptions require a clinical assessment — medication is not suitable for everyone
Use our GLP-1 weight loss calculator to explore potential weight loss at different doses, and our BMI calculator to check if you may be eligible.
- 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 diet jabs the same as Ozempic?
No. Both Wegovy and Ozempic contain semaglutide, but Ozempic is licensed for type 2 diabetes (doses up to 2mg) and is not approved for weight loss in the UK. Wegovy is specifically licensed for weight management at higher doses (up to 2.4mg). Using Ozempic for weight loss is off-label and not recommended. Always use the licensed product prescribed by your healthcare provider.
Are diet jabs available on the NHS?
Yes, diet jabs are available through NHS specialist tier 3 weight management services, but access is limited and varies significantly by region. Your GP can refer you if eligible. Many areas have long waiting lists. Private online prescribing is an alternative route available without NHS referral, though this involves a cost.
How much weight will I lose with diet jabs?
Individual results vary significantly. Clinical trials showed average weight loss of 15–21% of body weight, but this depends on your starting weight, dose, adherence, diet, and exercise. Weight loss occurs alongside a reduced-calorie diet and increased physical activity. Your prescriber can give personalised guidance based on your health.
What are the side effects of diet jabs?
Common side effects include nausea, diarrhoea, constipation, and stomach pain — usually temporary and often improve as your body adjusts. Less common side effects include fatigue, headache, and injection site reactions. Serious side effects are rare but include severe stomach pain (possible pancreatitis) and gallbladder problems. Discuss side effect concerns with your GP or prescriber.
Can I buy diet jabs without a prescription?
No. Diet jabs (Wegovy, Mounjaro, Saxenda) are all prescription-only medicines in the UK. You cannot purchase them without a valid prescription from a UK-licensed prescriber. Any offer to sell them without a prescription is illegal. Always use a GPhC-registered pharmacy with a qualified prescriber to ensure medication safety and authenticity.
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.