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
Does B12 Help With Weight Loss in the UK?
B12 plays a genuine role in metabolism and energy production, but on its own it is not a weight loss solution. If you have a B12 deficiency, correcting it can improve energy levels and support your weight loss efforts — but B12 supplementation without a deficiency won't directly cause weight loss. For adults in the UK seeking effective weight management help, prescription medications like Mounjaro and Wegovy have strong clinical evidence. Understanding the difference between B12's metabolic role and proven weight loss treatments is essential before you make health decisions.
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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 Medications With Clinical Evidence
If you're looking for evidence-based weight management in the UK, prescription medications offer clinically proven results. B12 supplementation alone is not recognised as a weight loss medication by the NHS or NICE. However, two GLP-1 receptor agonist medications are approved for weight loss in the UK:
- Mounjaro (tirzepatide) — a dual GIP and GLP-1 agonist. In clinical trials, adults lost an average of 15–21% of their body weight over 72 weeks, alongside a reduced-calorie diet and increased activity.
- Wegovy (semaglutide) — a GLP-1 agonist. Clinical trials showed average weight loss of approximately 15% of body weight at the maximum dose.
- Saxenda (liraglutide) — a daily GLP-1 injection. Evidence supports modest but consistent weight loss.
All three are prescription-only medicines requiring clinical assessment. You can check your eligibility using our free GLP-1 weight loss calculator to see potential outcomes at different doses. Eligibility typically includes a BMI of 30 or above, or 27 or above with weight-related health conditions like type 2 diabetes or high blood pressure.
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.
How to Access Weight Loss Support in the UK
There are two routes to prescription weight loss treatment in the UK:
- NHS route: Speak to your GP about referral to a tier 3 specialist weight management service. This may involve waiting lists in some regions, but treatments are free on the NHS.
- Private route: Licensed prescribers offer online consultations, typically available within days. A private prescription costs £150–£320 per month depending on dose and medication.
Your GP can help you understand which weight loss medication suits your health profile, or you can book a private consultation with a UK-licensed prescriber. Use our free BMI calculator to establish your baseline, and track your progress with our free progress tracker once you begin treatment. Weight loss medications work best alongside reduced-calorie diet changes and increased physical activity — medication supports your efforts, not replaces them.
- 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 deficiency cause weight gain?
B12 deficiency can slow metabolism and cause fatigue, which may make weight loss harder. If you have confirmed B12 deficiency, correcting it can restore energy and support weight management. However, B12 supplementation in people without deficiency is not an effective weight loss treatment.
What is the difference between B12 and prescription weight loss medication?
B12 is a vitamin your body needs for energy and nerve function. GLP-1 medications like Wegovy and Mounjaro actively reduce appetite and change how your body processes food. Only GLP-1 medications have clinical evidence for significant weight loss; B12 alone does not.
Can I get weight loss medication on the NHS in the UK?
Yes. NICE has approved tirzepatide (Mounjaro) and semaglutide (Wegovy) for NHS use through specialist tier 3 weight management services. Access varies by region and waiting times can be lengthy. Your GP can refer you to your local service.
Who is eligible for prescription weight loss medication in the UK?
Adults with a BMI of 30 or above, or 27 or above with weight-related health conditions (type 2 diabetes, hypertension, sleep apnoea), may be eligible. A licensed prescriber or GP must assess whether the medication is appropriate for your individual health.
Which weight loss medication is most effective in the UK?
Both Mounjaro and Wegovy have strong clinical evidence. Mounjaro (dual mechanism) showed slightly higher average weight loss in trials (~21% vs ~15%), but results vary significantly between individuals. Your prescriber will recommend based on your health profile and needs.
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.