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 Are Weight Loss Frinks?
Weight loss frinks — commonly called "weight loss jabs" or "slimming injections" — are prescription-only injectable medicines licensed in the UK for weight management. The most widely discussed are GLP-1 receptor agonists like Wegovy (semaglutide) and dual GIP/GLP-1 medications like Mounjaro (tirzepatide). These medications may help reduce appetite and support weight loss when combined with a reduced-calorie diet and increased physical activity. Access in the UK is through NHS specialist weight management services or private prescription following a clinical assessment. Results vary between individuals, and these are serious medications with potential side effects that require careful medical supervision.
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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.
How Do Weight Loss Frinks Work?
Weight loss frinks are GLP-1 receptor agonist injections that mimic hormones naturally produced in your gut. They work by signalling to your brain that you feel full, reducing appetite and food cravings. They also slow how quickly food leaves your stomach, helping you feel satisfied after smaller meals.
The two main types available in the UK are:
- Wegovy (semaglutide) — a once-weekly GLP-1 injection. Clinical trials showed participants lost an average of approximately 15% of their body weight over 68 weeks alongside a reduced-calorie diet and increased physical activity.
- Mounjaro (tirzepatide) — a once-weekly dual GIP and GLP-1 injection. In clinical trials, participants lost an average of 15–21% of body weight depending on dose.
Both are prescription-only medicines. They are not insulin and work differently from diabetes medications, though people with type 2 diabetes may also benefit from weight loss medication prescribed by their GP or specialist.
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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.
UK Eligibility and Access for Weight Loss Frinks
In the UK, you may be eligible for prescription weight loss medication if you have a BMI of 30 or above, or a BMI of 27–29.9 with a weight-related health condition such as type 2 diabetes, high blood pressure, or obstructive sleep apnoea. Use our free BMI calculator above to check your personal BMI instantly.
Access routes: NHS access is through specialist tier 3 weight management services — your GP can refer you, though waiting lists vary significantly by region. Private access is available through GPhC-registered online pharmacies following an online clinical assessment. A prescriber will assess whether a weight loss frink is suitable for you based on your individual health, medications, and medical history. Weight loss frinks are always used alongside lifestyle changes, not as a replacement for them.
- 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 weight loss frinks safe?
Weight loss frinks are prescription-only medicines approved by the MHRA. Like all medications, they have potential side effects — commonly nausea, diarrhoea, and constipation, especially when starting or increasing doses. Serious side effects are rare but can include pancreatitis. Your GP or prescriber will assess whether they're safe for you specifically, and you'll be monitored during treatment.
How much weight will I lose with a weight loss frink?
Individual results vary significantly. Clinical trials showed average weight loss of 14–21% of body weight, but some people lose more or less. Weight loss depends on your starting weight, the dose you take, your diet, physical activity level, and how your body responds. Your results cannot be predicted in advance — a prescriber can discuss realistic expectations based on available evidence.
What's the difference between weight loss frinks and Ozempic?
Both Wegovy and Ozempic contain semaglutide, but they're different medicines. Ozempic is licensed for type 2 diabetes management (up to 2 mg dose). Wegovy is specifically licensed for weight management (up to 2.4 mg dose). Ozempic is not licensed for weight loss in the UK — using it for weight loss is off-label. Wegovy is the correct licensed weight management version.
Can I get weight loss frinks on the NHS?
Yes — the NHS has approved tirzepatide (Mounjaro) and semaglutide (Wegovy) for weight management. Access is through specialist tier 3 weight management services, typically by GP referral. However, availability varies significantly by region (ICB), and waiting lists can be several months to over a year in many areas. Private access without NHS waiting lists is available through registered online prescribers.
How do I track my weight loss progress?
Track your weight loss journey using our free progress tracker on this page — log your weight, measurements, and progress notes over time. Combine this with our free BMI calculator to see how your BMI changes as you lose weight. This helps you monitor progress beyond just the scales, as weight loss may include changes in body composition alongside genuine fat loss.
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.