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 Losing Weight Injections?
Losing weight injections are prescription-only medications that help regulate appetite and support weight management in UK adults. Also known as weight loss jabs or slimming injections, these are GLP-1 receptor agonist medications licensed specifically for weight management. They work by mimicking natural hormones that signal fullness to the brain, potentially helping you eat less and feel satisfied with smaller portions. Unlike fad diets, they're prescribed following a clinical assessment and work alongside sustainable dietary changes and increased physical activity for best results.
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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 Do Weight Loss Injections Work?
Weight loss injections are GLP-1 receptor agonist medications that mimic a natural hormone produced in your gut after eating. This hormone signals your brain that you're full and helps regulate blood sugar levels. The two main licensed options in the UK are Wegovy (semaglutide) and Mounjaro (tirzepatide), available through NHS specialist weight management services or private prescribing.
These injections help by: slowing how quickly food leaves your stomach, reducing appetite and food cravings, helping you feel fuller after eating less, and supporting better appetite control throughout the day. Clinical trials showed that adults using these medications alongside a reduced-calorie diet and increased physical activity lost an average of 14–21% of their body weight over 68–72 weeks—though individual results vary significantly. Your GP or a licensed prescriber can assess whether a weight loss injection is appropriate for your personal health situation.
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 Injections
In the UK, you may be eligible for prescription weight loss injections if you have a BMI of 30 or above, or a BMI of 27–29.9 with at least one weight-related health condition (such as type 2 diabetes, high blood pressure, or sleep apnoea). Use our free BMI calculator above to check your personal BMI instantly. Lower BMI thresholds apply if you're of South Asian, Chinese, Black African, or Black Caribbean heritage, as these groups face higher health risks at lower weights.
Access is available through two routes: NHS specialist weight management services (via referral from your GP, though waiting lists vary by region) or private prescribing (following an online clinical assessment with a UK-licensed prescriber). Either way, a clinical assessment is required before prescription. Weight loss injections are always used alongside lifestyle changes, not instead of them.
- 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 available on the NHS?
Yes, GLP-1 injections like Wegovy and Mounjaro are available through NHS specialist weight management services. However, access requires referral from your GP and assessment by a tier 3 specialist service. Waiting times vary significantly by region (ICB). Private prescribing is also available without NHS referral.
How much weight can I lose with weight loss injections?
Clinical trials showed an average weight loss of 14–21% of body weight over 68–72 weeks, alongside a reduced-calorie diet and physical activity. Individual results vary considerably. Some people lose more, others less. Weight loss injections work best combined with sustainable lifestyle changes, not as standalone treatment.
What are the side effects of weight loss injections?
Common side effects include nausea, diarrhoea, vomiting, and constipation—especially when starting or increasing doses. Most side effects improve over time. Serious side effects are rare but can include severe stomach pain (possible pancreatitis) or allergic reactions. Your prescriber will discuss all risks before starting treatment.
Do weight loss injections work without diet and exercise?
No. Weight loss injections are most effective when combined with a reduced-calorie diet and increased physical activity. They help reduce appetite and support better food choices, but sustainable weight loss requires lifestyle changes. Try our free GLP-1 weight loss calculator to see projected results with medical support alongside lifestyle changes.
Is there a difference between Wegovy and Mounjaro for losing weight?
Both are prescription-only and effective for weight loss, but they work slightly differently. Wegovy (semaglutide) is a GLP-1 agonist. Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist, meaning it activates two hormone pathways. Clinical trials showed Mounjaro may help slightly more weight loss on average, but individual results vary. Your prescriber will advise which suits you best.
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.