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
Do B12 Shots Help With Weight Loss?
B12 injections are sometimes marketed as weight loss aids, but the evidence for this is limited. Vitamin B12 is essential for energy, metabolism, and nerve function, but having normal B12 levels does not directly cause weight loss. If you are deficient in B12, supplementing it may improve energy and metabolism — but this is different from using B12 as a standalone weight loss treatment. If you are looking for evidence-based prescription weight management in the UK, our GLP-1 weight loss calculator can help you explore medically-supported options with proven clinical trial data.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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.
What Does B12 Actually Do?
Vitamin B12 (cobalamin) is a water-soluble vitamin crucial for red blood cell formation, DNA synthesis, and nervous system function. It is also involved in energy metabolism — your body needs B12 to convert food into usable energy.
B12 deficiency can cause:
- Fatigue and low energy
- Brain fog and concentration problems
- Weakness and numbness
- Anaemia (low red blood cell count)
If you are B12 deficient, correcting the deficiency through injections or supplements may improve energy levels and general wellbeing. However, this is correcting a medical problem, not creating a weight loss effect. Studies show that B12 supplementation does not lead to weight loss in people with normal B12 levels. The NHS does not recommend B12 injections for weight loss — only for diagnosed deficiency.
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.
B12 vs Prescription Weight Loss Medication
If you are looking for evidence-based weight management support in the UK, prescription weight loss medications are far more established than B12 for weight loss. Medications like Mounjaro and Wegovy are GLP-1 or GIP/GLP-1 receptor agonists that have demonstrated significant weight loss in clinical trials — on average 15–21% of body weight with Mounjaro, and around 15% with Wegovy.
These are prescription-only medicines requiring a clinical assessment from a UK-licensed prescriber or NHS specialist service. Try our free BMI calculator to check your eligibility for weight management support, and use our weight converter if you want to track your weight in stone, kilograms, or pounds. For a personalised assessment of what might work for you, your GP can refer you to an NHS weight management service.
- 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.
Can B12 injections help me lose weight?
Not directly. B12 injections correct deficiency and may improve energy, but studies show they do not cause weight loss in people with normal B12 levels. The NHS does not recommend B12 injections as a weight loss treatment.
What is B12 actually used for in the UK?
B12 injections treat diagnosed deficiency, which can cause fatigue, anaemia, and neurological symptoms. Your GP can test your B12 levels. If deficient, injections may improve energy — but this is medical treatment, not weight loss.
Are there weight loss injections that actually work in the UK?
Yes. Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only GLP-1 medications with strong clinical evidence. Mounjaro helped participants lose an average of 15–21% of body weight in trials, alongside diet and exercise changes. Both require a prescription and clinical assessment.
How do GLP-1 weight loss injections differ from B12?
GLP-1 medications like Wegovy activate hormones that reduce appetite and support feeling fuller after smaller meals. B12 does not have this mechanism. GLP-1 medications have multiple clinical trials proving weight loss; B12 does not for weight loss specifically.
How do I access prescription weight loss medication on the NHS?
Ask your GP for a referral to a tier 3 specialist weight management service. Eligibility typically requires a BMI of 30 or above, or 27+ with weight-related health conditions. NHS availability varies by region. Private prescribing is also available through online assessments with UK-licensed prescribers.
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.