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
Do Weight Loss Injections Actually Work?
Yes, weight loss injections do work for many people — but they're not a effective solution. Prescription medications like Mounjaro and Wegovy have shown meaningful results in clinical trials when combined with diet and exercise. In the UK, these are prescription-only medicines available through NHS specialist services or private prescribing. Individual results vary significantly. Our GLP-1 weight loss calculator can help you understand potential outcomes, whilst our BMI calculator shows where you stand now and what healthy targets look like for your height.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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: What Works
Three prescription weight loss injections are currently licensed in the UK for weight management in eligible adults:
- Mounjaro (tirzepatide) — a dual GIP and GLP-1 receptor agonist. Clinical trials (SURMOUNT-1) showed average weight loss of 15–21% of body weight at the highest dose over 72 weeks.
- Wegovy (semaglutide) — a GLP-1 receptor agonist. STEP-1 trials showed average weight loss of approximately 14.9% of body weight at the maximum dose over 68 weeks.
- Saxenda (liraglutide) — a once-daily GLP-1 injection. Evidence supports meaningful weight loss, typically 4–8% body weight reduction.
All three work by reducing appetite, increasing fullness, and supporting healthier eating patterns. Importantly, these results were achieved alongside a reduced-calorie diet and increased physical activity. Weight loss injections amplify the effect of lifestyle changes — they don't replace them. Our weight loss calculator above can show you potential outcomes at different dose levels.
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 Started
In the UK, weight loss injections are available through two main routes. NHS access is through tier 3 specialist weight management services — your GP can refer you, though waiting lists vary significantly by region. Private access is through online consultations with UK-licensed prescribers; no NHS referral needed, though costs apply (typically £129–£320 monthly depending on dose).
Eligibility for both routes is similar: a BMI of 30 or above, or 27–29.9 with weight-related health conditions like type 2 diabetes, high blood pressure, or sleep apnoea. South Asian, Chinese, Black African, or Black Caribbean adults may have lower BMI thresholds. Your GP can advise on NHS eligibility and referral options, or you can explore private prescribing through an online assessment. Use our BMI calculator to check your starting point.
- 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.
Do weight loss injections work without diet and exercise?
No. Clinical trials showed weight loss results were achieved alongside reduced-calorie diet and increased physical activity. Injections enhance these lifestyle changes but don't replace them. Without dietary changes and movement, results will be significantly reduced. They're a tool to support your efforts, not a standalone solution.
How long does it take to see results with weight loss injections?
Most people begin noticing appetite reduction within the first 1–2 weeks. Measurable weight loss typically becomes apparent after 4–8 weeks. Clinical trials measured results over 68–72 weeks at full dose. Results vary — some lose weight faster, others slower. Consistency with your injection schedule and lifestyle changes matters significantly.
Are weight loss injections safe in the UK?
Yes, when prescribed appropriately following clinical assessment. All UK-licensed weight loss injections (Mounjaro, Wegovy, Saxenda) are approved by the MHRA. Side effects are common but usually temporary — nausea, constipation, and diarrhoea are most frequent. Serious complications are rare. Always discuss medical history, current medications, and family history with your prescriber.
Will I regain weight after stopping weight loss injections?
Weight regain is possible after stopping, particularly if lifestyle changes aren't maintained. Clinical evidence suggests that people who continue healthy eating and exercise patterns after stopping maintain more weight loss than those who revert to previous habits. Weight loss injections work best as part of a sustained lifestyle change, not a temporary fix.
Can I get weight loss injections on the NHS in my area?
NHS availability varies significantly by region (ICB). Some areas have accessible tier 3 weight management services; others have long waiting lists or limited provision. Ask your GP about local specialist services and waiting times. If NHS access is limited, private prescribing is an alternative. Check with your GP or a GPhC-registered online prescriber about your options.
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.