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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Understanding Weight Loss Whoosh and UK Medication Options
Weight loss whoosh is a term used to describe rapid, noticeable drops in body weight that can happen during any weight loss journey—often after a period of slower progress. If you're exploring weight management in the UK, prescription medications may be available to support your efforts. This guide explains how weight loss works, what prescription options exist for eligible adults, and how to find out if you qualify for treatment through the NHS or private prescribing.
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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 Prescription Weight Management Options
Three prescription medications are currently licensed in the UK for weight management in adults: Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). All three work by activating GLP-1 hormone pathways that help regulate appetite and food intake.
- Mounjaro: A once-weekly injection with a dual GIP and GLP-1 mechanism. Clinical trials showed an average weight loss of around 15–21% of body weight over 72 weeks, though individual results vary significantly.
- Wegovy: A once-weekly GLP-1 injection with an average weight loss of approximately 15% of body weight in clinical trials.
- Saxenda: A once-daily GLP-1 injection, though less commonly prescribed than Mounjaro or Wegovy.
Eligibility typically requires a BMI of 30 or above, or 27 or above with weight-related health conditions such as type 2 diabetes, high blood pressure, or cardiovascular disease. These medications work alongside reduced-calorie diet and increased physical activity—they are not replacements for lifestyle changes.
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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.
NHS Access vs Private Prescribing and Next Steps
In the UK, weight loss medication is available through two routes. NHS access involves referral to a specialist tier 3 weight management service by your GP; however, waiting lists can be lengthy and availability varies significantly by region. Private prescribing is available through GPhC-registered online providers following an online clinical assessment—faster access but with associated costs.
To find out if you're eligible, use our free BMI calculator above to check your current BMI, then speak with your GP about referral to specialist weight management services or ask about private prescribing options. Your GP can also assess whether any weight loss medication is appropriate for your individual health situation. Calculate your BMI now and use our GLP-1 weight loss calculator to explore projected weight loss at different medication doses.
- 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 exactly is weight loss whoosh?
Weight loss whoosh refers to sudden, more noticeable drops in body weight after a period of slower progress. This can happen with or without medication and is normal during any weight loss journey. It's often related to fluid loss, fat loss, or changes in how your body processes weight. Individual patterns vary significantly.
Am I eligible for prescription weight loss medication in the UK?
You may be eligible if you have a BMI of 30 or above, or 27 or above with a weight-related health condition like type 2 diabetes, high blood pressure, or sleep apnoea. Adults of South Asian, Chinese, Black African, or Black Caribbean heritage may have lower eligibility thresholds. Speak with your GP for personalised eligibility assessment.
How much weight can I expect to lose with GLP-1 medication?
Clinical trials showed average weight loss of 15–21% of body weight depending on the medication and dose, though individual results vary considerably. Some people lose more, some less. Weight loss depends on the medication dose, how long you take it, your diet, physical activity, and individual factors. Results are not assured.
What's the difference between NHS and private weight loss medication in the UK?
NHS access requires GP referral to specialist services but has regional waiting lists. Private prescribing is available through online providers without NHS referral but involves costs. Both require clinical assessment. NHS access is free but slower; private is faster but paid.
How do I get started with weight loss medication if I'm interested?
First, check your BMI using our free BMI calculator on this page. Then either ask your GP about NHS specialist weight management services, or speak with your GP about private prescribing options. A qualified prescriber will assess whether medication is suitable for your individual health and circumstances.
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.