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 Is the Safest Weight Loss Injection in the UK?
Weight loss injections available in the UK are prescription-only medications that have undergone rigorous safety testing and regulatory approval. The safest options for weight management are Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide)—all licensed by the MHRA and approved for use in UK adults. These medications work by mimicking natural hormones that regulate appetite and blood sugar. Safety depends on proper medical assessment, correct dosing, and lifestyle support. If you're considering weight loss medication, your GP can discuss which option is most appropriate for your individual health profile and weight loss goals.
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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.
UK-Licensed Weight Loss Injections: Options and Evidence
Three prescription weight loss injections are currently licensed in the UK:
- Mounjaro (tirzepatide) — A dual GIP and GLP-1 receptor agonist, injected once weekly. Clinical trials showed average weight loss of 15–21% body weight over 72 weeks when combined with diet and exercise.
- Wegovy (semaglutide) — A GLP-1 receptor agonist, injected once weekly. The STEP trials demonstrated approximately 15% average weight loss at the maximum 2.4mg dose.
- Saxenda (liraglutide) — A GLP-1 receptor agonist, injected once daily. Approved for weight management, it helps reduce appetite and supports portion control.
All three medications are prescription-only and require a clinical assessment before prescribing. Eligibility typically includes adults with a BMI of 30 or above, or 27+ with weight-related health conditions such as type 2 diabetes, high blood pressure, or sleep apnoea. Individual suitability depends on your medical history, current medications, and personal health circumstances.
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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.
NHS vs Private Access: Finding the Right Path for You
In the UK, weight loss injections are available through two routes:
NHS access: Available through specialist tier 3 weight management services following GP referral. NICE has approved these medications for NHS use, but availability varies significantly by region and local ICB funding. Many areas have substantial waiting lists.
Private access: Available through GPhC-registered online prescribing services following a clinical consultation. No NHS referral is required. Speak with your GP first about eligibility and suitability—they can advise whether prescription weight loss medication is appropriate for you and help you understand your options. Whether NHS or private, the key to safe and effective weight loss is combining medication with sustainable dietary changes, increased physical activity, and regular progress monitoring using tools like our free BMI calculator and weight loss projection calculator.
- 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 injections safe?
Yes, when prescribed appropriately. Mounjaro, Wegovy, and Saxenda are MHRA-approved and have undergone rigorous clinical trials. Safety depends on medical assessment before prescribing, correct dosing, and monitoring for side effects. Common side effects include nausea and digestive changes, which typically ease over time. Always inform your prescriber of all medications and medical conditions.
How much weight can I expect to lose with a weight loss injection?
Clinical trials show average weight loss of 15–21% body weight, depending on the medication and dose. However, individual results vary significantly. Weight loss is most effective when combined with a reduced-calorie diet and increased physical activity. Use our free GLP-1 weight loss calculator to estimate potential results based on your current weight and chosen medication.
How do I know if I'm eligible for weight loss injections on the NHS?
NHS eligibility typically requires a BMI of 30 or above, or 27+ with weight-related health conditions such as type 2 diabetes or high blood pressure. Eligibility varies by region. Speak with your GP about referral to a specialist weight management service. They can assess whether these medications are appropriate for you based on your individual health profile.
What's the difference between Mounjaro and Wegovy?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist, while Wegovy (semaglutide) is a GLP-1 agonist only. Mounjaro showed slightly higher average weight loss in trials (15–21% vs 15%), and both are once-weekly injections. The choice depends on your individual health circumstances and prescriber assessment. Neither is inherently "safer"—both are well-tolerated when prescribed appropriately.
Can I get weight loss injections privately if I'm not eligible for NHS treatment?
Yes. Private prescribing through GPhC-registered online services is available to eligible adults following a clinical consultation. However, you should discuss this with your GP first. They can advise on suitability, potential interactions with other medications, and ensure you're making an informed decision. Private costs vary by dose and provider (approximately £129–£320 monthly).
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.