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
B12 For Weight Loss — What You Need To Know
B12 is a vitamin essential for energy metabolism and nerve function, but taking B12 alone won't cause weight loss. If you're looking for evidence-based weight loss support in the UK, prescription medications like Mounjaro and Wegovy are available for eligible adults. This guide explains B12's role in weight management, the truth about B12 supplements, and the prescription weight loss options your GP can discuss with you.
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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 Options For Eligible Adults
If you're seeking effective weight management in the UK, prescription weight loss medication is available through the NHS and private prescribing for eligible adults. These evidence-based options include:
- Mounjaro (tirzepatide) — a dual GIP and GLP-1 receptor agonist shown in clinical trials to help adults lose an average of 15–21% of body weight when combined with lifestyle changes
- Wegovy (semaglutide) — a GLP-1 injection that supported around 15% average body weight loss in clinical trials
- Saxenda (liraglutide) — a daily GLP-1 injection option
Eligibility typically includes adults with a BMI of 30 or above, or BMI 27–29.9 with weight-related health conditions. Access through NHS weight loss services requires referral to a specialist tier 3 service, though private online prescribing is also available for those who meet clinical criteria. Calculate your BMI using our free BMI calculator above to see where you stand, then discuss options with your GP.
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 — How To Access Weight Loss Support
The NHS funds prescription weight loss medication through specialist weight management services, but availability and waiting times vary significantly by region. Your GP can assess your eligibility and refer you to your local service if appropriate. Private prescribing offers faster access — a UK-licensed prescriber conducts an online clinical assessment and, if suitable, issues a prescription dispensed by a registered pharmacy.
Whichever route you choose, prescription weight loss treatment works best alongside a reduced-calorie diet and increased physical activity. Our free GLP-1 weight loss calculator can help you estimate potential results at different doses. Most importantly, speak to your GP about which option is right for your circumstances.
- 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.
Will B12 supplements alone help me lose weight?
B12 is essential for energy and metabolism, but supplementing B12 won't cause weight loss unless you have a deficiency. If your B12 levels are normal, extra B12 won't speed up weight loss. For evidence-based weight loss support, prescription medications like Mounjaro and Wegovy are far more effective for eligible adults.
What do prescription weight loss injections actually do?
Mounjaro and Wegovy work by activating GLP-1 (and GIP, in Mounjaro's case) hormone pathways. This reduces appetite, helps you feel fuller after smaller meals, and slows stomach emptying. Clinical trials showed these medications help adults lose 15–21% of body weight when combined with diet and exercise.
Am I eligible for NHS weight loss medication?
Generally, you may be eligible if you have a BMI of 30 or above, or BMI 27–29.9 with weight-related health conditions like type 2 diabetes, high blood pressure, or sleep apnoea. Your GP can assess your eligibility and refer you to a specialist weight management service if appropriate for your situation.
How long does it take to see weight loss results with prescription medication?
Most people begin to see measurable weight loss within 4–8 weeks of starting treatment, though individual results vary. Prescription weight loss medications work best alongside a reduced-calorie diet and regular physical activity — they support these changes, they don't replace them.
What's the difference between Mounjaro and Wegovy for weight loss?
Both are once-weekly injections approved for UK weight management. Mounjaro is a dual GIP and GLP-1 agonist (potentially more potent), while Wegovy is a GLP-1-only medication. Clinical trials showed Mounjaro achieved slightly higher average weight loss, but individual responses vary. Your prescriber will assess which suits 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.