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
What Do Weight Loss Injections Do?
Weight loss injections are prescription-only medications that help manage body weight by reducing appetite and supporting feelings of fullness. Available in the UK through NHS specialist services and private prescribing, these medications work alongside diet and exercise changes. Three main options are licensed for weight management: Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). Clinical trials show these medications may help eligible adults lose significant weight when combined with lifestyle changes. Understanding how they work and who qualifies is the first step toward exploring whether weight management through medication is right for you.
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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 How They Work
GLP-1 receptor agonist medications mimic a natural hormone your gut produces after eating. They help regulate appetite by signalling to your brain that you feel full, slow how quickly food leaves your stomach, and support blood sugar control. Three prescription injections are licensed for weight management in the UK:
- Mounjaro (tirzepatide) — Dual GIP and GLP-1 agonist, once-weekly injection, doses from 2.5mg to 15mg. Clinical trials showed average weight loss of 15–21% body weight over 72 weeks.
- Wegovy (semaglutide) — GLP-1 agonist, once-weekly injection, doses up to 2.4mg. Clinical trials showed average weight loss of approximately 15% body weight.
- Saxenda (liraglutide) — GLP-1 agonist, daily injection, doses up to 3mg. Earlier licensed option for weight management in the UK.
These medications work best when combined with reduced-calorie diet and increased physical activity. Individual results vary significantly. Try our free GLP-1 weight loss calculator to explore potential outcomes at different doses.
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.
Eligibility and How to Access Weight Loss Injections in the UK
To be eligible for prescription weight loss injections in the UK, you typically need a BMI of 30 or above, or BMI of 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or cardiovascular disease. Adults of South Asian, Chinese, Black African, or Black Caribbean heritage may qualify at lower BMI thresholds due to increased health risk at these levels.
NHS access: Referral to your local tier 3 specialist weight management service through your GP. Availability and waiting times vary significantly by region.
Private access: Online consultation with a UK-licensed prescriber, followed by prescription dispensed by a registered pharmacy. Check your BMI using our free BMI calculator to understand your starting point, then discuss options with your GP.
- 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.
How quickly do weight loss injections work in the UK?
Weight loss typically begins within the first few weeks, with most noticeable changes after 12–16 weeks of consistent use. Clinical trials measured results over 68–72 weeks. Results depend on dose, duration of treatment, and lifestyle changes. Your prescriber will monitor progress and adjust doses as needed.
Are weight loss injections available on the NHS?
Yes. Tirzepatide (Mounjaro) and semaglutide (Wegovy) are approved for use within NHS specialist weight management services. Access requires referral from your GP to tier 3 services. Availability varies by region and waiting times can be lengthy in some areas. Private prescribing is also available.
What side effects do UK weight loss injections have?
Common side effects include nausea, diarrhoea, constipation, and stomach discomfort—typically mild and temporary. These usually improve as your body adjusts. Serious side effects are rare but can include severe stomach pain (pancreatitis) or gallbladder problems. Your prescriber will discuss all risks before treatment.
Can I switch between Mounjaro and Wegovy?
Switching between medications is possible but must be managed by your prescriber. There is no official conversion chart—any change requires medical assessment. Mounjaro uses a dual mechanism (GIP+GLP-1) while Wegovy uses GLP-1 only, so effects differ. Discuss alternatives with your GP or prescriber.
Do I need to diet and exercise while using weight loss injections?
Yes. Weight loss injections work best alongside reduced-calorie diet and increased physical activity. They support appetite control and fullness, making dietary changes easier—but they are not a substitute for lifestyle changes. Track your progress with our free progress tracker to stay motivated. ```
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.