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
Pros and Cons of Weight Loss Injections
Weight loss injections like Mounjaro and Wegovy are prescription-only medications that have become increasingly popular for weight management in the UK. But are they right for you? This guide explores the evidence-based benefits and limitations of GLP-1 and GIP receptor agonist medications, helping you understand what to expect, what challenges to prepare for, and how they fit into a realistic weight loss strategy. Use our free GLP-1 weight loss calculator to estimate potential outcomes at different doses.
10,000+ calculations today ยท NHS-aligned thresholds ยท 100% free
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/mยฒ).
While BMI isn't a perfect measure โ it doesn't account for muscle mass, bone density, or fat distribution โ 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 โ 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.
The Main Benefits of Weight Loss Injections
Clinically proven effectiveness: In clinical trials, weight loss injections helped participants lose an average of 15โ21% of their body weight over 68โ72 weeks, significantly more than diet and exercise alone. Results vary between individuals, but many people experience meaningful improvements in weight and related health conditions.
Once-weekly convenience: Mounjaro and Wegovy are both administered once weekly by subcutaneous injection โ easier than daily medications or restrictive diets. Many people find this more sustainable than constant dietary discipline.
Health improvements beyond weight: Clinical trials showed improvements in blood pressure, blood sugar control, and cardiovascular risk markers โ not just weight loss. These benefits can reduce the risk of heart disease and type 2 diabetes.
Support for behaviour change: By reducing appetite and cravings, these medications can make dietary changes feel more manageable, helping you establish healthier eating patterns long-term.
Available through NHS: Weight loss injections are now accessible through NHS specialist weight management services in some areas, though availability varies by region.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care โ 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 โ 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 โ completely free.
The Main Disadvantages and Challenges
Significant side effects: Nausea, vomiting, diarrhoea, and constipation are common, especially when starting or increasing doses. Most people adjust over time, but some cannot tolerate the medication.
Weight regain after stopping: Clinical evidence suggests that weight often returns if you stop the injection โ these are maintenance medications, not permanent supports. Sustainable results require ongoing use or established lifestyle change.
Cost and access barriers: Private treatment costs ยฃ120โยฃ320 monthly depending on dose. NHS access is limited to specialist services with long waiting lists in many areas, creating significant inequality.
Not suitable for everyone: Pregnancy, severe gastroparesis, personal or family history of thyroid cancer, and allergy to tirzepatide or semaglutide are contraindications. People on insulin or sulphonylureas need careful dose adjustment.
Long-term data gaps: These medications are relatively new for weight management โ long-term safety data beyond 3 years is still emerging.
- 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 โ 5mg โ 7.5mg โ 10mg โ 12.5mg โ 15mg
- GLP-1 receptor agonist
- Up to 15โ17% body weight loss (STEP trials)
- Weekly injection, 5-step dose escalation
- NHS & private prescription available
- Doses: 0.25mg โ 0.5mg โ 1mg โ 1.7mg โ 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 | 15โ22.5% | 12โ17% |
| Key trial | SURMOUNT-1 (2022) | STEP 1 (2021) |
| Max dose | 15 mg weekly | 2.4 mg weekly |
| Escalation period | 20โ32 weeks | 16โ20 weeks |
| Administration | Weekly injection (pen) | Weekly injection (pen) |
| NHS availability | Private prescription only | NHS & private |
| Approx. private cost | ยฃ150โยฃ250/month | ยฃ150โยฃ300/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 โ 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.
Do weight loss injections actually work?
Yes โ clinical trials show weight loss injections help people lose an average of 15โ21% of body weight over 68โ72 weeks, alongside reduced-calorie diet and exercise. Individual results vary significantly. They are more effective than diet and exercise alone, but weight regain is common if the medication is stopped.
How much weight can I expect to lose?
This varies widely between individuals and depends on starting weight, dose, genetics, diet, and exercise. Clinical trial averages are 15โ21%, but some people lose less, some more. Use our free weight loss calculator to estimate a personalised projection based on your circumstances.
What are the most common side effects?
Nausea, vomiting, diarrhoea, and constipation occur in more than 1 in 10 people. Most side effects are mild to moderate and improve over weeks to months as your body adjusts. Serious side effects are rare but can include pancreatitis and severe allergic reactions.
Can I get weight loss injections on the NHS?
Yes, through NHS tier 3 specialist weight management services if you meet eligibility criteria. However, availability varies significantly by region, and waiting lists can be very long. Private access is available through GPhC-registered online prescribers with clinical assessment, but costs ยฃ120โยฃ320 monthly.
What happens to my weight when I stop the injection?
Weight regain is common if you stop medication without established lifestyle changes. Clinical evidence suggests most people regain some weight โ these are long-term maintenance medications, not short-term treatments. Success requires either ongoing medication or sustained dietary and activity 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.