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
Injections for Fat Loss: What You Need to Know
Fat loss injections are prescription-only medicines that may help support weight management in UK adults. These medications, known as GLP-1 receptor agonists, work by affecting appetite and how your body processes food. They're available through the NHS and private prescribing in the UK, though eligibility and access vary. This guide explains how they work, who can use them, and what to expect. Our free BMI calculator can help you understand your current weight status and whether you might be eligible for weight management support.
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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 Fat Loss Injections Work
GLP-1 receptor agonist medications mimic a natural hormone your gut produces after eating. This hormone helps regulate appetite, slows how quickly food leaves your stomach, and signals fullness to your brain. The most commonly prescribed fat loss injections in the UK are Wegovy (semaglutide) and Mounjaro (tirzepatide). Both are once-weekly injections given under the skin. Clinical trials have shown that people using these medications, alongside a reduced-calorie diet and increased physical activity, may lose an average of 15–21% of their body weight over several months. However, individual results vary significantly. These injections are prescription-only medicines and require a clinical assessment before being prescribed. They are not clinically supported solutions—they work best when combined with healthy eating habits and regular exercise.
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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.
UK Eligibility and Access
In the UK, fat loss injections may be prescribed to adults with a BMI of 30 or above, or 27 or above if you have weight-related health conditions such as type 2 diabetes, high blood pressure, or sleep apnoea. Access through the NHS is via referral to a specialist tier 3 weight management service—waiting times vary significantly by region. Private access is available through UK-licensed online prescribing services following a clinical assessment. Use our free weight converter to check your current weight in kg, and our GLP-1 weight loss calculator to understand potential outcomes at different doses. Your GP can advise on NHS eligibility and referral pathways in your area.
- 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 fat loss injections safe?
Fat loss injections are prescription medicines approved by UK regulators (MHRA) when used as directed. Like all medications, they have potential side effects—most commonly nausea, diarrhoea, and vomiting, especially when starting. Serious side effects are rare. A prescriber will assess your individual health before prescribing to ensure safety.
Can I get fat loss injections on the NHS?
Yes, but access is limited. NHS prescribing is through specialist tier 3 weight management services, not standard GP practice. You'll need a referral from your GP and may face waiting lists. Private prescribing is available more quickly through registered online services.
How much weight will I lose with fat loss injections?
Clinical trials show average weight loss of 15–21% over several months when combined with diet and exercise. However, individual results vary—some people lose more, others less. Weight loss isn't assured and depends on your starting weight, dose, adherence, and lifestyle changes.
Are fat loss injections permanent?
No. These injections help manage weight while you're using them. Weight management requires ongoing effort—combining the injection with healthy eating and physical activity. If you stop the injection without maintaining lifestyle changes, weight may return over time.
What's the difference between Wegovy and Ozempic?
Both contain semaglutide, but Wegovy is licensed specifically for weight management in the UK and uses the 2.4mg dose. Ozempic is licensed for type 2 diabetes (up to 2mg) and is not approved for weight loss. Always ensure your prescription specifies Wegovy if weight management is the goal.
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.