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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Diet Drinks And Weight Loss — What Works In The UK
Diet drinks are often promoted as a weight loss tool, but the evidence is mixed. While they contain fewer calories than regular sugary drinks, they may not directly support weight loss for everyone. For adults in the UK struggling with weight management, prescription medications like Mounjaro and Wegovy are now available through NHS specialist services or private prescribing. These GLP-1 and dual-action injections work differently from diet drinks — they address appetite and hunger directly. This guide explains what the evidence shows about diet drinks and introduces prescription weight loss options available to eligible UK adults.
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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 Prescription Weight Loss Options
For UK adults with a BMI of 30 or above, or 27–29.9 with weight-related health conditions, prescription weight loss medication may be recommended as part of a comprehensive weight management approach. Three main options are currently licensed:
- Mounjaro (tirzepatide) — a dual GIP and GLP-1 receptor agonist injected once weekly. Clinical trials showed average weight loss of 15–21% of body weight over 72 weeks alongside diet and exercise.
- Wegovy (semaglutide) — a GLP-1 receptor agonist injected once weekly. Clinical evidence showed average weight loss of approximately 15% of body weight at the maximum dose.
- Saxenda (liraglutide) — a GLP-1 receptor agonist injected daily, with similar weight loss results to Wegovy.
All three are prescription-only medicines requiring clinical assessment. Unlike diet drinks, these medications work by reducing appetite, increasing satiety, and supporting better food choices when combined with lifestyle changes. Individual results vary significantly — some people respond better than others. Your prescriber will assess whether you're eligible and which option suits your health profile best.
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 — And Getting Started
In the UK, prescription weight loss medication is available through two main routes:
- NHS access: Through referral to a tier 3 specialist weight management service. Availability varies by region and waiting lists can be lengthy. Your GP can discuss whether you meet eligibility criteria for NHS services.
- Private access: Through online consultations with UK-licensed prescribers, followed by prescription dispensing by GPhC-registered pharmacies. This route is faster but involves private cost, typically £129–£320+ per month depending on dose.
The most important first step is a conversation with your GP about your weight management goals and health. They can assess your eligibility, discuss all available options (including lifestyle support, diet drinks, or prescription medication), and refer you to specialist services if appropriate. Use our free BMI calculator above to understand your current BMI category, and our GLP-1 weight loss calculator to explore projected outcomes if medication is suitable for you.
- 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 diet drinks effective for weight loss in the UK?
Diet drinks contain fewer calories than regular sugary drinks, which may help with calorie reduction. However, evidence suggests they don't directly cause weight loss — they're a tool, not a solution. Some research suggests artificial sweeteners may even maintain sweet taste preferences. For reliable weight loss, a calorie deficit through whole dietary changes is more effective. For significant weight loss support, prescription medication or NHS weight management services are recommended.
What's the difference between diet drinks and prescription weight loss medication?
Diet drinks reduce calorie intake but don't address hunger or appetite directly. Prescription weight loss medications like Mounjaro and Wegovy work on appetite-regulating hormones in the brain, reducing cravings and promoting satiety. They're clinically proven to support 15–clinically studied weight loss in trials. However, medication requires prescription and clinical assessment — it's not suitable for everyone.
Who is eligible for prescription weight loss medication in the UK?
UK adults with a BMI of 30 or above, or 27–29.9 with weight-related health conditions (type 2 diabetes, high blood pressure, cardiovascular disease, sleep apnoea), may be eligible. South Asian, Chinese, Black African, and Black Caribbean adults may qualify at lower BMI thresholds due to higher health risks. Always discuss eligibility with your GP or a licensed prescriber.
How long does it take to see weight loss with prescription medication?
Weight loss typically begins within the first 4–8 weeks as doses are increased. Most significant loss occurs between weeks 8–16. Clinical trials measured weight loss over 12–16 weeks, with results continuing to improve over 52–72 weeks. Individual timelines vary — some people lose weight steadily, others see results more gradually.
Can I use diet drinks alongside prescription weight loss medication?
Yes, diet drinks can be part of a reduced-calorie diet when taking prescription weight loss medication. However, they're not necessary — most people find reduced appetite from medication makes beverage choices simpler. Always discuss your full diet and any concerns with your prescriber or GP. Focus on whole foods, adequate hydration, and consistent activity for best results.
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.