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
Weight Loss Magnesium: What Works in the UK
Magnesium supplements are sometimes marketed for weight loss, but there's no strong evidence they cause meaningful weight loss on their own. However, if you're interested in weight management, the UK has prescription-only medications licensed specifically for this purpose. These medications work differently from supplements and have clinical trial evidence behind them. If you have a BMI of 30 or above, or 27 or above with weight-related health conditions, you may be eligible for prescription weight loss treatment. Your GP can assess whether you're a suitable candidate and discuss your options.
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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 Medications
Three prescription-only medications are currently licensed in the UK for weight management in adults:
- Mounjaro (tirzepatide) — a once-weekly injection that activates two hormone pathways (GIP and GLP-1). In clinical trials, participants lost an average of 15–21% of their body weight over 72 weeks.
- Wegovy (semaglutide) — a once-weekly GLP-1 injection. Clinical trials showed average weight loss of approximately 15% of body weight.
- Saxenda (liraglutide) — a daily GLP-1 injection offering similar weight management support.
All three are prescription-only and require a clinical assessment before being prescribed. They work by helping regulate appetite and promoting satiety, and are most effective when combined with reduced-calorie diet and increased physical activity. Use our GLP-1 weight loss calculator to explore potential outcomes at different doses, and try our BMI calculator to check if you might be eligible based on your current measurements.
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.
Getting Weight Loss Medication in the UK
There are two main routes to access prescription weight loss medication in the UK:
- NHS route: Ask your GP for a referral to a specialist tier 3 weight management service. Access varies significantly by region, and waiting lists can be long in some areas.
- Private route: Consult a UK-licensed prescriber online, followed by prescription dispensing through a registered pharmacy.
Eligibility is assessed individually based on your BMI, weight-related health conditions (such as type 2 diabetes, high blood pressure, or sleep apnoea), and overall health profile. Your GP is the best starting point — they can discuss whether prescription medication is appropriate for you and explain both NHS and private options. Sustainable weight management in the UK involves combining medication with lifestyle changes, regular physical activity, and dietary changes.
- 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 magnesium actually help with weight loss?
Magnesium is an essential mineral important for many body functions, but evidence does not support magnesium supplements as an effective weight loss tool on their own. It may support general health and muscle function, but weight loss requires a calorie deficit. If you're looking for evidence-based weight management support, prescription medications like Mounjaro and Wegovy have stronger clinical trial evidence.
Who is eligible for prescription weight loss medication in the UK?
Generally, adults with a BMI of 30 or above, or a BMI of 27–29.9 with weight-related health conditions (such as type 2 diabetes, high blood pressure, or sleep apnoea), may be eligible. South Asian, Chinese, Black African, and Black Caribbean adults may qualify at lower BMI thresholds. Your GP or a licensed prescriber can assess your individual eligibility.
What's the difference between Mounjaro and Wegovy?
Both are once-weekly injections for weight management, but they work differently. Mounjaro is a dual GIP and GLP-1 receptor agonist, while Wegovy is a GLP-1-only medication. Clinical trials suggest Mounjaro may produce slightly higher average weight loss (15–21% vs 15%), but individual results vary significantly. A prescriber can advise which is more suitable for you.
Can I get weight loss medication through the NHS?
Yes. Weight loss medications are available through NHS specialist tier 3 weight management services, but access varies significantly by region and waiting times can be long. Your GP can refer you to your local specialist service. Alternatively, private online prescribers offer faster access if you meet eligibility criteria and can afford the cost.
How much weight can I expect to lose with prescription medication?
Clinical trials show average weight loss of 15–21% of body weight depending on the medication and dose — but individual results vary considerably. Weight loss occurs alongside a reduced-calorie diet and increased physical activity. Our weight loss calculator can help estimate potential outcomes, but your prescriber is the best source for personalised expectations based on your health profile.
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.