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
Is The Weight Loss Injection Safe?
Yes, weight loss injections are safe when prescribed and used correctly by eligible adults. These prescription medications, including Wegovy (semaglutide) and Mounjaro (tirzepatide), have been through rigorous clinical trials and are approved by the MHRA for weight management in the UK. Like all medicines, they do have side effects, but these are generally manageable. Your GP or a licensed prescriber will assess whether a weight loss injection is appropriate for you based on your individual health, medical history, and eligibility. Individual results vary, and these medications work best alongside lifestyle changes.
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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 Safe Are Weight Loss Injections?
Weight loss injections licensed in the UK have demonstrated safety in large clinical trials. Wegovy (semaglutide) was evaluated in the STEP trials involving thousands of participants, and Mounjaro (tirzepatide) was assessed in the SURMOUNT trials. Both showed that the medications are safe for appropriate candidates when used as prescribed. Common side effects include nausea, diarrhoea, and constipation — these typically decrease over time as your body adjusts. More serious side effects are rare but can include pancreatitis or gallbladder problems. The MHRA (Medicines and Healthcare products Regulatory Authority) continues to monitor these medications closely through pharmacovigilance. Every prescription is issued following a clinical assessment to ensure the medication is safe for your specific situation. Your prescriber will review your medical history, current medications, and any contraindications before issuing a prescription.
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.
Important Safety Considerations
Weight loss injections are prescription-only medicines — they are not available over-the-counter. You cannot take them if you are pregnant, planning pregnancy, or breastfeeding, as safety data in these groups is limited. If you have a history of thyroid cancer, pancreatitis, or severe gastroparesis, these medications may not be suitable. You should inform your prescriber of all current medications, as GLP-1 injections may affect how oral contraceptives and other medicines work. Regular monitoring is recommended, particularly if you have type 2 diabetes or take insulin. Never share your injection with anyone else, and always follow the prescribed dose schedule. If you experience severe abdominal pain, vision changes, or signs of allergic reaction, seek immediate medical attention.
- 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 are the most common side effects of weight loss injections?
The most common side effects are nausea, diarrhoea, vomiting, and constipation. Most people find these decrease within the first few weeks. Taking the injection at the same time each week and adjusting your diet (smaller portions, lower-fat meals) often helps. Inform your GP if side effects persist or become severe.
Can weight loss injections damage your pancreas?
Pancreatitis (pancreas inflammation) is a rare but serious side effect. If you experience sudden severe stomach pain spreading to your back, seek immediate medical attention. This risk is why prescribers assess your medical history and exclude those with a history of pancreatitis. Most people using these injections safely do not develop pancreatitis.
Are weight loss injections safer than weight loss surgery?
Both have different risk profiles. Injections are non-surgical and reversible, but require ongoing use and have side effects. Surgery is more invasive with immediate risks but may provide faster results. Your GP can discuss which option is safer and more appropriate for your individual circumstances.
How do I know if a weight loss injection is safe for me personally?
A licensed prescriber will conduct a clinical assessment reviewing your medical history, current medications, BMI, and any weight-related health conditions. They will exclude you if you have contraindications like thyroid cancer, pregnancy, or severe kidney disease. Use our GLP-1 weight loss calculator and BMI calculator to understand your baseline, then discuss with your prescriber.
What should I do if I experience side effects from my weight loss injection?
Contact your prescriber or GP immediately if side effects are severe or persistent. Most side effects are manageable by adjusting your diet or dose. Never stop taking your injection without medical guidance. Your prescriber may adjust your dose, change injection timing, or recommend alternative approaches to manage symptoms effectively.
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.