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
Drastic Weight Loss Side Effects and UK Medication Options
gradual weight management can cause unwanted side effects, from nutritional deficiencies to gallstones. In the UK, if you're struggling with weight management, prescription medications like Mounjaro and Wegovy offer evidence-based alternatives to drastic dieting. These GLP-1 weight management options support sustainable weight loss alongside lifestyle changes, reducing the risk of dangerous side effects associated with extreme calorie restriction. Understanding your options—and your eligibility—starts with a conversation with your GP or a licensed prescriber.
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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 Management Medications and How They Work
Drastic weight loss from extreme dieting carries real health risks: muscle loss, nutrient deficiencies, gallstones, hormonal disruption, and metabolic slowdown. Prescription weight loss medications in the UK offer a safer, clinically-supported approach to weight management.
Three medications are licensed in the UK for adults with a BMI of 30 or above (or 27+ with weight-related health conditions like type 2 diabetes or hypertension):
- Mounjaro (tirzepatide) — dual GIP and GLP-1 receptor agonist; once-weekly injection; clinical trials showed average weight loss of 15–21% of body weight
- Wegovy (semaglutide) — GLP-1 receptor agonist; once-weekly injection; average weight loss approximately 15% of body weight in trials
- Saxenda (liraglutide) — GLP-1 receptor agonist; once-daily injection; established option with long safety data
Unlike crash diets, these medications work by reducing appetite and supporting feeling fuller after smaller meals—allowing sustainable weight loss without dangerous calorie restriction. Individual results vary, and all are used alongside a reduced-calorie diet and increased physical activity. Our GLP-1 weight loss calculator can help you explore potential outcomes at different doses.
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 Access vs Private Prescription Weight Loss in the UK
NHS route: Tier 3 specialist weight management services can prescribe weight loss medication following GP referral. Availability varies significantly by region (ICB), and waiting lists can be lengthy in many areas. Check with your GP whether your NHS area offers this support.
Private route: GPhC-registered online pharmacies dispense weight loss medication following a clinical assessment by a UK-licensed prescriber—no NHS referral needed. You can explore eligibility without waiting. Use our free BMI calculator to check your starting point, then speak with a prescriber about whether prescription weight loss treatment is right for you. Weight loss medications are most effective when combined with behaviour change and lifestyle support.
If you're considering weight loss medication, your first step is understanding your BMI and eligibility. Calculate your BMI now using the free tool on this page. Then discuss your options with your GP or a licensed prescriber—they can assess your individual health, explain potential side effects, and help you choose the safest, most effective approach. Sustainable weight loss prevents the serious complications of both obesity and drastic dieting.
- 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 are the main side effects of drastic weight loss dieting?
gradual weight management from extreme calorie restriction can cause muscle loss, nutrient deficiencies, fatigue, gallstones, hormonal imbalance, weak bones, and metabolic slowdown. The NHS recommends losing no more than 0.5–1 kg per week for safety.
How do prescription weight loss medications like Mounjaro avoid these side effects?
Mounjaro and Wegovy reduce appetite and support feeling fuller after meals, allowing gradual, sustainable weight loss without severe calorie restriction. This preserves muscle and nutrient intake better than crash dieting. Individual results vary.
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 BMI of 27–29 with weight-related health conditions such as type 2 diabetes, high blood pressure, or heart disease. A GP or licensed prescriber will assess your individual circumstances.
What's the difference between NHS and private weight loss medication in the UK?
NHS prescriptions come through tier 3 specialist services (waiting lists vary by region). Private prescriptions are available through online clinics following a clinical assessment, without NHS referral. Both require a UK-licensed prescriber.
Is weight loss medication safe for long-term use?
Mounjaro and Wegovy have strong clinical safety data. They're designed for long-term use as part of sustained weight management. Your prescriber will monitor you regularly and adjust doses if needed.
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.