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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Low Carbohydrate Diet And Weight Loss — UK Medication Options
A low carbohydrate diet is one of the most researched dietary approaches for weight management in the UK. It can be effective for sustainable weight loss when combined with calorie awareness and physical activity. For adults who struggle with diet alone, prescription weight loss medication is now available through the NHS and private prescribers. This guide explains how low carbohydrate eating works, how it compares to other weight loss strategies, and what medication options are available if you're eligible for treatment. Use our free BMI calculator above to check where you currently stand, and explore whether prescription support might be right for you.
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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 Prescription Weight Loss Options For Low Carb Diet Support
For adults following a low carbohydrate diet who want additional support, three prescription weight loss medications are licensed in the UK: Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide).
These are GLP-1 receptor agonist medications (or dual GIP/GLP-1 in the case of Mounjaro) that work alongside dietary changes to support weight management. In clinical trials, participants combining these medications with dietary changes — including low carbohydrate approaches — experienced meaningful weight loss.
- Mounjaro: once-weekly injection, average weight loss 15–21% of body weight
- Wegovy: once-weekly injection, average weight loss approximately 15% of body weight
- Saxenda: once-daily injection, suitable for those preferring daily dosing
All three are prescription-only and require a clinical assessment before being prescribed. You can estimate potential weight loss outcomes using our free GLP-1 weight loss calculator, which shows projected results at different doses.
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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 Check Your Eligibility
NHS access: Prescription weight loss medication is available through specialist tier 3 weight management services, typically accessed via GP referral. However, availability varies significantly by region and waiting lists can be lengthy. Your GP can advise whether you meet NHS eligibility criteria (BMI 30 or above, or 27–29.9 with weight-related health conditions like high blood pressure or type 2 diabetes).
Private access: Available through online prescribing services following a clinical assessment. No NHS referral needed, though costs vary by dose and provider. Both routes require a licensed prescriber to assess suitability based on your individual health history.
The best first step is to speak with your GP about your weight loss goals and ask whether prescription medication might support your low carbohydrate diet efforts. They can also calculate your BMI and discuss eligibility.
- 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.
Does a low carbohydrate diet work better than other diets for weight loss in the UK?
Low carbohydrate diets are effective for weight loss and are well-researched. Short-term weight loss outcomes are similar to standard calorie-restricted diets. Long-term success depends on adherence and individual factors including lifestyle, genetics, and metabolic health. Evidence suggests any diet you can sustain will work better than one you abandon.
Can I combine a low carbohydrate diet with weight loss medication like Mounjaro or Wegovy?
Yes, prescription weight loss medications are designed to be used alongside lifestyle changes, including dietary approaches. Many people combine low carbohydrate eating with GLP-1 medication for enhanced results. Your prescriber will advise you on the best combination for your individual circumstances.
What BMI do I need to be eligible for prescription weight loss medication in the UK?
Generally, adults with a BMI of 30 or above are eligible. Those with a BMI of 27–29.9 and at least one weight-related health condition (such as type 2 diabetes, high blood pressure, or sleep apnoea) may also qualify. Use our BMI calculator above to find your personal BMI, then speak with your GP about eligibility.
How much weight can I expect to lose on prescription medication combined with low carb diet?
Clinical trials show average weight loss of 15–21% of body weight with medications like Mounjaro, and approximately 15% with Wegovy, when combined with diet and activity changes. However, individual results vary significantly. Our weight loss calculator can help you estimate potential outcomes at different doses.
Should I try a low carbohydrate diet before asking my GP about weight loss medication?
Many people benefit from dietary changes alone. However, if you've tried diet and exercise without sufficient results, speaking with your GP about prescription options is worthwhile. They can assess whether medication might help and discuss your individual circumstances. There's no requirement to exhaust diet-only approaches first.
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.