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
How Quickly Do B12 Shots Work for Weight Loss?
B12 shots alone are not clinically proven to cause weight loss in people with normal B12 levels. While B12 is essential for metabolism and energy, taking extra B12 through injections will not lead to weight loss unless you have a pre-existing B12 deficiency. For effective weight management in the UK, your GP may recommend prescription weight loss medication or lifestyle changes backed by evidence. Let's explore what the science actually shows about B12, metabolism, and weight loss.
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 Do for Metabolism?
Vitamin B12 (cobalamin) plays a crucial role in energy production and supports your metabolism by helping convert food into energy. However, this does not mean that B12 injections will automatically help you lose weight. Key points about B12 and weight loss:
- B12 injections may boost energy levels if you have a deficiency, which could theoretically support more physical activity
- Studies show no significant weight loss from B12 injections in people with adequate B12 levels
- NHS guidance does not recommend B12 injections as a weight loss treatment
- Your GP can test your B12 levels if you feel unusually fatigued
- Genuine B12 deficiency (pernicious anaemia, certain diets) requires treatment, but this is a medical condition — not a weight loss strategy
For evidence-based weight loss medication nhs access or prescription weight loss uk options, your GP can discuss medications licensed for weight management.
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.
What About B12 and Weight Loss Injections?
You may have seen "B12 weight loss injections" advertised online. These are often marketed as fat-burning solutions, but they are not the same as glp-1 weight loss medications like Wegovy or Mounjaro. The confusion arises because:
- B12 injections are inexpensive and widely available — making them easy to market
- GLP-1 weight loss injections are prescription-only and clinically proven in trials
- Wegovy (semaglutide) showed average weight loss of ~15% body weight in clinical trials
- B12 alone has no such evidence for weight loss
Our GLP-1 weight loss calculator can help you understand projected weight loss with evidence-based medications. Your GP can assess eligibility for prescription weight loss injections uk through specialist services.
- 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 a B12 injection help me lose weight if I don't have a deficiency?
No. If your B12 levels are normal, additional B12 injections will not cause weight loss. B12 supports energy and metabolism, but extra B12 does not create a calorie deficit. Only a calorie deficit — through diet, activity, or prescription medication — leads to weight loss. Your GP can test your B12 level if you have symptoms of deficiency like fatigue or numbness.
What's the difference between B12 and GLP-1 weight loss injections?
B12 is a vitamin supplement; GLP-1 medications like Wegovy are prescription-only weight management drugs. GLP-1 injections reduce appetite, increase satiety, and help create a calorie deficit. Clinical trials show GLP-1 medications produce average weight loss of 15–21% body weight. B12 injections are not proven for weight loss. Both require different assessments from your GP or a prescriber.
How quickly does Wegovy (the actual weight loss injection) work?
Wegovy is a GLP-1 receptor agonist that starts working within days to weeks to reduce appetite. Most people notice appetite changes within 1–2 weeks. Measurable weight loss typically begins within 2–4 weeks, but individual results vary. The medication is taken as a once-weekly injection and requires a prescription following clinical assessment.
What are NHS options for weight management if B12 doesn't work?
The NHS offers tiered weight management support: Tier 1 includes self-help tools and community programmes, Tier 2 offers behaviour change support through your GP, Tier 3 includes specialist multidisciplinary services where prescription weight loss medication may be considered. Ask your GP about referral to specialist weight management services or explore evidence-based approaches like reduced-calorie diet and increased physical activity.
Can I use the BMI calculator to check if I'm eligible for prescription weight loss treatment?
Our free BMI calculator can help you understand your current BMI and see where you fall on the NHS health weight ranges. A BMI of 30 or above, or 27 or above with weight-related health conditions, may qualify you for prescription weight loss treatment. Use the calculator, then speak with your GP about your individual eligibility and what options are available through NHS services or private prescribing.
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.