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 and Weight Loss — What You Need to Know
B12 is a vitamin essential for energy and metabolism, but B12 supplements alone are not proven for weight loss in otherwise healthy adults. If you're exploring weight management in the UK, prescription medications like Mounjaro and Wegovy have strong clinical evidence. This guide explains the difference between B12 supplementation and prescription weight loss medication, helping you understand your options for sustainable weight management through your GP or private prescribing.
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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 Eligible Adults
If you're interested in weight management in the UK, several prescription weight loss medications are available through NHS specialist services or private online prescribing. These are far more evidence-based than B12 supplementation alone:
- Mounjaro (tirzepatide) — a dual GIP and GLP-1 injection. Clinical trials showed adults lost an average of 15–21% of body weight over 72 weeks alongside a reduced-calorie diet and increased physical activity.
- Wegovy (semaglutide) — a GLP-1 injection. Average weight loss in trials was approximately 15% of body weight at the standard dose.
- Saxenda (liraglutide) — a daily GLP-1 injection. Approved for weight management in eligible UK adults with BMI 30 or above, or 27–29.9 with weight-related health conditions.
Eligibility varies by individual health circumstances. Use our free GLP-1 weight loss calculator to explore potential outcomes, then speak with your GP about suitability.
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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.
How to Access Weight Loss Medication in the UK
NHS access: Weight loss medications are available through tier 3 specialist weight management services. Your GP can refer you, though waiting lists vary by region. NICE has approved tirzepatide (Mounjaro) for NHS use in eligible adults.
Private access: GPhC-registered online prescribers offer Mounjaro, Wegovy, and Saxenda following a clinical assessment. No NHS referral needed, though costs range from approximately £129–£320 monthly depending on dose.
Before considering any prescription medication, calculate your BMI using our free BMI calculator to understand your current weight category. Your GP can then discuss whether prescription weight loss support is appropriate for you alongside lifestyle 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 B12 supplementation help with weight loss?
B12 is essential for energy and metabolism, but there is no strong clinical evidence that B12 supplements alone cause weight loss in otherwise healthy adults. If you have a diagnosed B12 deficiency, supplementation corrects that deficiency and may improve energy levels, which can support physical activity. However, for evidence-based weight loss, prescription medications like Mounjaro and Wegovy have clinical trial support.
What is the difference between B12 and GLP-1 weight loss medication?
B12 is a vitamin that supports energy metabolism. GLP-1 medications like Wegovy and Mounjaro are prescription receptor agonists that reduce appetite and support feeling fuller after meals. GLP-1 medications have strong clinical trial evidence for weight loss (15–21% average). B12 alone does not have this evidence, though it supports overall health.
Can I get Mounjaro or Wegovy through the NHS in the UK?
Yes, both Mounjaro and Wegovy are available through NHS specialist weight management services. You'll need a GP referral to tier 3 services. Availability and waiting times vary significantly by region. Alternatively, private prescribing is available without NHS referral through GPhC-registered online prescribers.
How do I know if I'm eligible for prescription weight loss medication in the UK?
Eligibility typically requires a BMI of 30 or above, or 27–29.9 with weight-related health conditions like type 2 diabetes, high blood pressure, or cardiovascular disease. For South Asian, Chinese, Black African, or Black Caribbean adults, lower thresholds may apply. Your GP or a licensed prescriber can assess your individual suitability.
What is the best weight management approach in the UK?
The most effective approach combines dietary changes, increased physical activity, and—if eligible—prescription medication support. The NHS recommends losing 0.5–1 kg per week for sustainable results. Our free progress tracker can help you log your journey, while our BMI calculator shows your baseline health category. Your GP can discuss the full range of options available to you.
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.