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
Understanding Obesity Injections and Weight Health
An obesity injection is a prescription-only medication that may help support weight management for eligible UK adults. If you're concerned about your weight and health, it's important to understand what these injections are, whether you might be eligible, and what support is available through the NHS and privately. This guide explains the health context, the evidence, and your options.
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Calculate Your BMI Instantly
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.
Health Risks Linked to Excess Weight
Excess weight significantly increases the risk of serious health conditions. According to NHS data, being overweight or obese is linked to type 2 diabetes, heart disease, high blood pressure, certain cancers, and sleep apnoea. At severe obesity levels, the risk of type 2 diabetes is up to 80 times higher than healthy weight. Even modest amounts of extra weight can affect joints, breathing, and quality of life. The good news: losing just 5–10% of body weight can reduce blood pressure, improve blood sugar control, and lower cholesterol. Use our free BMI calculator above to check where your weight falls on the NHS scale. A BMI of 30 or above, or 25–29.9 with weight-related health conditions, may warrant discussion with your GP about support options.
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.
Support Available in the UK
The NHS offers a structured weight management pathway. Start with your GP to discuss your health and weight. If eligible, you may be referred to a tier 3 specialist weight management service where prescription medications, including obesity injections, may be considered alongside diet and activity changes. Privately, prescription weight loss injections are available through online assessment with UK-licensed prescribers, though costs apply. Whichever route you take, sustainable weight loss combines medication (if appropriate) with lifestyle changes. Track your progress with our free progress tracker, and use our weight converter to understand your weight across different measurements.
- 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.
What is an obesity injection?
An obesity injection is a prescription-only medication, such as a GLP-1 receptor agonist (e.g. Mounjaro or Wegovy), that may help reduce appetite and support weight management. These are licensed in the UK for adults with a BMI of 30 or above, or 27+ with weight-related health conditions. They work alongside diet and activity changes, not instead of them.
How do I know if I'm overweight or obese?
According to NHS guidelines, a healthy BMI is 18.5–24.9. An overweight BMI is 25–29.9, and obese is 30 or above. Use our free BMI calculator on this page to check your personal BMI instantly based on your height and weight. Remember, BMI is a screening tool and doesn't account for muscle mass.
Can I get an obesity injection on the NHS?
Yes, but access varies by region. You'll need referral from your GP to a specialist tier 3 or tier 4 weight management service. Waiting lists can be lengthy in some areas. Alternatively, prescription obesity injections are available privately through online prescribing services, though these involve a cost.
What are the main health risks of excess weight?
Excess weight increases risk of type 2 diabetes, cardiovascular disease, high blood pressure, certain cancers, sleep apnoea, and joint problems. At severe obesity, risk is significantly elevated. However, even small amounts of weight loss—around 5–10% of body weight—can meaningfully improve blood sugar, blood pressure, and cholesterol levels.
How quickly can I expect to lose weight with an obesity injection?
Clinical trials show average weight loss of 15–21% over several months alongside diet and activity changes, though individual results vary significantly. The NHS recommends losing 0.5–1 kg per week for sustainable results. Your prescriber will monitor your progress and adjust treatment as needed.
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.