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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Weight Loss By Dieting: Diet, Exercise & UK Medication Options
Losing weight through dieting remains one of the most effective and sustainable approaches to weight management in the UK. A calorie deficit — consuming fewer calories than you burn — is the fundamental principle that drives weight loss, typically resulting in around 0.5 to 1 kg loss per week according to NHS guidance. For eligible adults, prescription weight management medications like GLP-1 injections can complement dietary changes, but diet and lifestyle remain the foundation of successful, lasting weight loss. This guide covers evidence-based dieting strategies, medication options available in the UK, and how to determine if you're eligible for prescription support.
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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 Weight Loss Medications & Dieting Support
While reducing calorie intake through dieting is the primary driver of weight loss, prescription weight management medications are available in the UK for eligible adults as an additional tool. Three GLP-1 medications are currently licensed for weight management:
- Mounjaro (tirzepatide) — dual GIP and GLP-1 receptor agonist, once weekly injection, doses 2.5–15 mg. Clinical trials showed average weight loss of 15–21% body weight alongside diet and exercise.
- Wegovy (semaglutide) — GLP-1 receptor agonist, once weekly injection, doses 0.25–2.4 mg. Evidence from STEP trials demonstrated approximately 15% average body weight reduction.
- Saxenda (liraglutide) — GLP-1 receptor agonist, daily injection, doses 0.6–3 mg. Licensed for weight management in UK adults with BMI 30 or above, or 27–29.9 with weight-related health conditions.
All three are prescription-only medicines requiring clinical assessment. Medications work by reducing appetite, increasing satiety, and supporting adherence to a reduced-calorie diet — they do not replace dieting. Try our free GLP-1 weight loss calculator to estimate potential results at different doses alongside your dietary efforts.
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 with Weight Loss Support
Access to prescription weight management medication in the UK follows two routes:
- NHS route: Referral from your GP to a tier 3 specialist weight management service. Availability and waiting times vary significantly by region (integrated care board). Many areas have extended waiting lists.
- Private route: Online consultation with a UK-licensed prescriber through a GPhC-registered pharmacy. Available without NHS referral. Assessment typically takes 24–48 hours.
Before any medication prescription, a clinician will assess your BMI, health conditions, and suitability. Start by speaking with your GP about your weight management goals. They can discuss whether medication might help you alongside dieting, refer you to NHS services if appropriate, or discuss private options. Calculate your current BMI using our free BMI calculator to give your GP clear baseline information.
- 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 much weight can I lose by dieting alone without medication?
Sustainable dieting typically results in 0.5–1 kg (1–2 lbs) per week according to NHS guidance. Over 12 weeks, that's 6–12 kg. Results depend on your starting weight, calorie deficit, age, metabolism, and consistency. Faster loss is possible with larger deficits but increases muscle loss risk. Individual results vary significantly.
What makes a diet effective for weight loss?
An effective diet creates a calorie deficit — you consume fewer calories than you burn. The NHS recommends a deficit of approximately 500 kcal daily for 0.5 kg weekly loss. Sustainable approaches include portion control, increasing protein intake, reducing refined carbohydrates, and choosing whole foods. The "best" diet is one you can stick to long-term.
Who is eligible for prescription weight loss medication in the UK?
Adults with a BMI of 30 kg/m² or above, or 27–29.9 with weight-related health conditions (diabetes, high blood pressure, high cholesterol, sleep apnoea, cardiovascular disease). South Asian, Chinese, Black African, and Black Caribbean adults may be eligible at lower BMI thresholds. Age 18 and above. Pregnancy, breastfeeding, and certain medical conditions exclude eligibility.
Can I use weight loss medication instead of dieting?
No. Prescription weight loss medications like Mounjaro and Wegovy are designed to *support* dieting, not replace it. Clinical trials that demonstrated weight loss included participants following a reduced-calorie diet and increased physical activity. Medication works best alongside lifestyle changes.
How long does it take to see weight loss results?
With dieting, most people see noticeable changes within 2–4 weeks, though initial loss is often water weight. Measurable fat loss typically becomes apparent within 4–6 weeks of consistent calorie deficit. With prescription GLP-1 medication, dose escalation happens gradually over 16–20 weeks, with weight loss progressing throughout. Patience and consistency matter more than speed.
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.