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 In The UK?
Yes, prescription weight loss injections available in the UK are safe when prescribed and monitored by a qualified healthcare professional. These medications undergo rigorous safety testing and are regulated by the MHRA. The most commonly prescribed options—Mounjaro and Wegovy—have been used in clinical trials and are now used across the NHS and private weight management services. Like all prescription medicines, they do carry side effects and require a proper clinical assessment before use. Understanding how they work, who can take them, and what to expect helps you make an informed decision with your GP.
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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: Safety & Eligibility
Three prescription weight loss injections are currently licensed in the UK for adults with a BMI of 30 or above, or 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or cardiovascular disease:
- Mounjaro (tirzepatide) — a dual GIP and GLP-1 receptor agonist, administered once weekly at doses from 2.5 mg to 15 mg. Clinical trials showed average weight loss of 15–21% body weight.
- Wegovy (semaglutide) — a GLP-1 receptor agonist, administered once weekly at doses up to 2.4 mg. Clinical evidence demonstrates average weight loss around 15% body weight.
- Saxenda (liraglutide) — a GLP-1 agonist administered as a daily injection up to 3 mg, with similar efficacy to Wegovy.
All three are prescription-only medicines and require a clinical assessment to determine suitability. Individual results vary considerably, and these medications work best alongside dietary changes and increased physical activity for sustainable weight management.
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: How To Access Weight Loss Medication Safely
In the UK, prescription weight loss injections are available through two routes. The NHS route involves referral to a specialist tier 3 weight management service via your GP; availability and waiting times vary significantly by region. The private route offers faster access through registered online prescribing services following a clinical consultation—no NHS referral required.
Regardless of route, you'll undergo an assessment to confirm eligibility, discuss medical history, and ensure the medication is appropriate for you. Your GP can advise on NHS availability in your area. If you're considering private prescription, ensure the provider is GPhC-registered and the prescriber is UK-licensed. Both routes prioritise safety through proper medical oversight. Use our free BMI calculator above to check your current BMI and understand where you fall on NHS weight management 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.
What are the most common side effects of weight loss injections?
The most common side effects include nausea, diarrhoea, constipation, and stomach discomfort—especially during dose escalation. These often reduce over time as your body adjusts. Injection site reactions (redness or bruising) can occur but are usually mild. Serious side effects are rare but include severe abdominal pain (possible pancreatitis) or allergic reactions—seek immediate medical attention if these occur. Always inform your prescriber of any persistent side effects.
Can I get weight loss injections on the NHS?
Yes, the NHS prescribes weight loss injections through specialist tier 3 weight management services. Referral typically comes from your GP, and eligibility is assessed based on BMI and health conditions. However, availability varies significantly across UK regions, and waiting times can be lengthy. Ask your GP about availability in your area, or contact your local Integrated Care Board (ICB). Private prescription options are also available if NHS waiting times are prohibitive.
Who is eligible for weight loss injections in the UK?
You may be eligible if you're an adult with a BMI of 30 or above, or 25–29.9 with a weight-related health condition (type 2 diabetes, high blood pressure, cardiovascular disease, or sleep apnoea). For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, thresholds may be lower due to higher health risk at lower BMI. Pregnancy, severe kidney or pancreatic disease, and history of thyroid cancer are contraindications. A prescriber will assess your individual circumstances.
Do weight loss injections work without diet and exercise?
Weight loss injections are most effective when combined with dietary changes and increased physical activity. Clinical trials that demonstrated 15–clinically studied weight loss involved participants following reduced-calorie diets and activity plans alongside the medication. The injection supports appetite reduction and feeling fuller, but sustainable weight loss requires lifestyle changes too. Think of the medication as a tool to support your efforts, not a replacement for them.
How long do you take weight loss injections for?
Duration varies based on your individual goals and response. Some people take them for 12–24 months, while others continue longer-term. Your prescriber will monitor your progress and discuss goals regularly. If you stop taking the medication, weight loss may slow or reverse, particularly if lifestyle changes aren't maintained. The decision to continue, adjust, or stop is made between you and your healthcare team based on your health outcomes and preferences.
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.