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
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Are Weight Loss Injections Safe? What the NHS Recommends
Weight loss injections, also called GLP-1 medications, are prescription-only medicines approved by UK medical regulators for weight management. Three options are licensed in the UK: Mounjaro, Wegovy, and Saxenda. Clinical trials show these medications can help eligible adults lose weight alongside diet and exercise changes. Safety depends on proper medical assessment, correct dosing, and monitoring by a healthcare professional. This guide explains what the NHS recommends about weight loss injections in the UK, who is eligible, and how to access them safely through the NHS or private prescribing services.
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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 and Safety Evidence
Three prescription weight loss injections are currently licensed in the UK:
- Mounjaro (tirzepatide) — a dual GIP and GLP-1 receptor agonist injected once weekly. Clinical trials showed average weight loss of 15–21% of body weight over 72 weeks at the maximum dose.
- Wegovy (semaglutide) — a GLP-1 receptor agonist injected once weekly. STEP trial data showed average weight loss of approximately 15% of body weight at 68 weeks.
- Saxenda (liraglutide) — a GLP-1 receptor agonist injected once daily. Earlier clinical trials demonstrated average weight loss of 5–8% of body weight.
All three medications are subject to rigorous safety monitoring by the MHRA (UK Medicines and Healthcare Products Regulatory Agency). Before prescription, a healthcare professional will assess your eligibility, current health conditions, medications, and contraindications. Common side effects include nausea, diarrhoea, and constipation — typically mild and improve over time. Serious side effects are rare when used as prescribed. Use our GLP-1 weight loss calculator to understand projected outcomes at different doses based on clinical evidence.
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 Access vs Private Prescribing — How to Get Started
NHS route: You can access prescription weight loss medication through the NHS, but availability varies significantly by region. Ask your GP for a referral to a specialist weight management service (tier 3). Some areas have long waiting lists due to high demand. Your GP will assess whether you meet NHS eligibility criteria: BMI of 30 or above, or 27–29.9 with a weight-related health condition like type 2 diabetes, high blood pressure, or sleep apnoea.
Private route: GPhC-registered online prescribing services offer faster access. You'll complete an online consultation with a UK-licensed prescriber, who will assess your suitability. If approved, a prescription is issued and dispensed by a registered pharmacy. Check your personal eligibility using our BMI calculator above — this will help you understand whether your BMI qualifies under current thresholds.
- 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 GLP-1 weight loss injections safe for long-term use?
Clinical trials have tracked GLP-1 medications for up to 68–72 weeks with good safety profiles. Long-term safety data beyond 2 years is still being gathered. All medications require ongoing monitoring by a healthcare professional. If you're considering long-term use, discuss this with your prescriber, who will monitor your health regularly and adjust treatment as needed.
Can I get weight loss injections on the NHS in the UK?
Yes, weight loss injections are available on the NHS through specialist tier 3 weight management services. Your GP can refer you. However, waiting times vary by region and can be months to years. Private access through online prescribing services is faster but requires payment. Ask your GP about local NHS availability in your area.
What eligibility criteria do I need to meet for prescription weight loss treatment?
Adults with a BMI of 30 kg/m² or above are generally eligible. Those with a BMI of 27–29.9 may be eligible if they have weight-related health conditions such as type 2 diabetes, prediabetes, high blood pressure, or sleep apnoea. For South Asian, Chinese, Black African, or Black Caribbean adults, lower BMI thresholds may apply due to higher health risks at lower weights.
Are weight loss injections safe if I have other health conditions?
Weight loss injections are not suitable for everyone. Contraindications include pregnancy, breastfeeding, severe digestive problems, certain thyroid conditions, and personal or family history of medullary thyroid cancer. Before prescription, a healthcare professional will review your full medical history and all current medications to ensure safety.
What's the difference between weight loss injections available on the NHS and private prescribing?
The medications themselves are the same (Mounjaro, Wegovy, or Saxenda). The difference is access speed and cost. NHS prescribing is free but subject to long waiting lists and regional availability. Private prescribing is faster (usually within days) but involves a consultation fee and medication costs. Clinical safety monitoring applies in both cases.
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.