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
Are Slimming Injections Safe in the UK?
Yes, slimming injections (weight loss injections) are safe when prescribed and monitored by qualified healthcare professionals. In the UK, only licensed medications with proven safety records are approved for weight management. These prescription slimming injections work by mimicking natural hormones that help regulate appetite. However, like all medications, they have potential side effects and aren't suitable for everyone. Understanding your options, eligibility criteria, and how different injections work will help you make an informed decision with your GP or prescriber.
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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.
UK-Licensed Weight Loss Injections: Mounjaro, Wegovy & Saxenda
Three prescription weight loss injections are currently licensed in the UK: Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). Each has a different mechanism and dosing schedule.
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist administered once weekly (doses 2.5–15mg). Clinical trials showed participants lost an average of 15–21% body weight over 72 weeks. Wegovy (semaglutide) is a GLP-1-only injection, also once weekly (0.25–2.4mg), with average weight loss of approximately 15% in clinical trials. Saxenda (liraglutide) is a daily injection (0.6–3mg), also a GLP-1 agonist, typically producing 5–clinically studied weight loss.
All three are prescription-only medicines requiring clinical assessment before prescribing. Individual results vary significantly, and these medications work alongside a reduced-calorie diet and increased physical activity. Use our free GLP-1 weight loss calculator to estimate potential outcomes at different doses, and our BMI calculator to understand your current health status.
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.
NHS vs Private Access: How to Get Weight Loss Injections
NHS access is through tier 3 specialist weight management services following GP referral. Availability varies significantly by region, and waiting lists can be lengthy. Your GP will assess eligibility based on BMI (≥30, or ≥27 with weight-related health conditions) and other health factors.
Private access is available through GPhC-registered online pharmacies following an online clinical assessment with a UK-licensed prescriber. This route does not require NHS referral and prescriptions are issued if clinically appropriate. Costs range from approximately £129–£320 per month depending on dose and provider.
Both routes are equally safe — the key difference is availability and waiting times. Your prescriber (NHS or private) will monitor your progress, manage side effects, and adjust your dose as needed. Track your weight loss journey using our free progress tracker.
- 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 slimming injections safe long-term?
Yes, when prescribed and monitored by a qualified healthcare professional. Mounjaro and Wegovy have been studied for over 2 years in clinical trials with good safety profiles. However, they are prescription-only medicines with potential side effects. Long-term safety is monitored through ongoing prescriber check-ins, regular appointments, and symptom reporting. Your prescriber will decide if continued use is appropriate for you.
What are the most common side effects of weight loss injections?
The most common side effects are nausea, diarrhoea, vomiting, and constipation, especially when starting or increasing dose. These often improve over time. Less common side effects include headache, fatigue, dizziness, and injection site reactions. Serious side effects are rare but include severe stomach pain (possible pancreatitis) and gallbladder problems. Always report new symptoms to your prescriber immediately.
Who cannot take slimming injections?
Weight loss injections are not suitable for people under 18, those pregnant or breastfeeding, those with a personal or family history of thyroid cancer, or anyone allergic to the active ingredient. If you have severe gastroparesis, diabetes on insulin/sulphonylureas, or a history of pancreatitis, prescriber approval is essential. Your GP or prescriber will assess your full medical history before prescribing.
Do I need to diet and exercise while taking slimming injections?
Yes. Weight loss injections work best alongside a reduced-calorie diet and regular physical activity. They support appetite control and help you feel fuller, but they don't replace lifestyle changes. Clinical trials showed best results when participants combined injection therapy with diet and exercise. Your GP or weight management service can advise on appropriate calorie targets and activity levels.
How quickly will I see results with weight loss injections?
Results typically become noticeable within 4–8 weeks, though individual timelines vary. Most people continue to lose weight over 12–24 weeks as they adjust to the medication. The dose is often increased gradually, which may impact weight loss speed. Remember that weight loss is not linear — plateaus are normal. Tracking progress with measurements and how clothes fit can help during slower periods.
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.