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
Weight Loss Injections in the UK — What You Need to Know
Weight loss injections are prescription-only medicines that can support weight management in UK adults. The most commonly known options are Wegovy (semaglutide) and Mounjaro (tirzepatide), both licensed for weight management by the MHRA. These injections work by mimicking natural hormones that help regulate appetite and support feeling fuller after meals. They're typically used alongside dietary changes and increased physical activity, not as standalone treatments. Access in the UK is available through NHS specialist weight management services or private prescribing following a clinical assessment. Results vary significantly between individuals.
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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.
How Weight Loss Injections Work
Weight loss injections are GLP-1 receptor agonists — medications that activate the GLP-1 hormone pathway, which is naturally produced in your gut after eating. This mechanism may help:
- Reduce appetite and food cravings
- Support feeling fuller after smaller meals
- Slow how quickly food leaves your stomach
- Help regulate how your body uses fat
Wegovy (semaglutide) is a once-weekly GLP-1 injection. Mounjaro (tirzepatide) is also once-weekly but uses a dual GIP and GLP-1 mechanism, which activates two natural hormone pathways. In clinical trials, Mounjaro showed slightly higher average weight loss (approximately 15–21% of body weight) compared to Wegovy (approximately 15% of body weight) — though individual results vary considerably. Both require a prescription and must be prescribed by a UK-licensed healthcare professional following a clinical assessment. Our GLP-1 weight loss calculator can help you estimate potential weight loss at different doses, though results are always individual.
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.
Eligibility and NHS Access in the UK
To be eligible for prescription weight loss injections in the UK, you typically need a BMI of 30 kg/m² or above, or a BMI of 27–29.9 kg/m² with weight-related health conditions such as type 2 diabetes, high blood pressure, or cardiovascular disease. Lower thresholds may apply if you are of South Asian, Chinese, Black African, or Black Caribbean heritage.
NHS access: Referral to tier 3 specialist weight management services through your GP. Waiting times vary by region — some areas have significant waiting lists. Private access: Available through GPhC-registered online pharmacies following an online clinical assessment, without NHS referral. Use our BMI calculator to check your current BMI and understand whether you may be eligible for prescription weight loss support.
- 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 the same as Ozempic?
No. Ozempic contains semaglutide (the same active ingredient as Wegovy) but is licensed for type 2 diabetes management only — not for weight loss in the UK. Wegovy is the licensed weight management version of semaglutide, approved specifically for weight management. Using Ozempic for weight loss is off-label and not recommended. Always ask your prescriber which medication they are prescribing and confirm it is licensed for weight management.
How much weight can I expect to lose with a weight loss injection?
Clinical trials show average weight loss of 15–21% of body weight over 68–72 weeks, depending on the medication and dose — but individual results vary significantly. Some people lose more, some less. Weight loss occurs alongside a reduced-calorie diet and increased physical activity, not medication alone. Our weight loss calculator can give you a projection based on your current weight and the medication dose, though this is not assured.
What are the common side effects of weight loss injections?
The most common side effects are nausea, diarrhoea, vomiting, constipation, and stomach pain — typically most noticeable when starting or increasing dose. Most side effects reduce over time as your body adjusts. Less common side effects include fatigue, dizziness, headache, and injection site reactions. Serious side effects are rare but include severe stomach pain (possible pancreatitis) and gallbladder problems. Always report new or concerning symptoms to your GP or prescriber.
Can I get weight loss injections on the NHS?
Yes, NICE has approved tirzepatide (Mounjaro) and semaglutide (Wegovy) for NHS use. However, NHS access is through specialist tier 3 weight management services — not standard GP prescription. You must be referred by your GP and meet eligibility criteria. Availability and waiting times vary significantly by region. If NHS waiting times are long in your area, private prescribing is available as an alternative.
Do I need to follow a diet and exercise plan with weight loss injections?
Yes. Weight loss injections are most effective when combined with a reduced-calorie diet and increased physical activity. They are not standalone treatments — they support your efforts to eat healthier and move more by helping reduce appetite and cravings. Your prescriber will discuss dietary and lifestyle changes as part of your weight management plan. Track your progress with our free progress tracker to monitor both weight loss and lifestyle changes. --- ```
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.