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
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Nutritional Supplements for Weight Loss in the UK
Nutritional supplements are widely marketed for weight loss, but evidence for most is limited. This guide explains what the research actually shows about vitamins, minerals, and herbal supplements used for weight management in the UK. We'll compare these options with prescription weight loss medication and NHS-approved approaches. If you're exploring weight management options, understanding the evidence behind different approaches—from dietary supplements to prescription treatments—is essential for making informed 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.
Common Weight Loss Supplements and Their Evidence Base
Several nutritional supplements are marketed for weight loss in the UK, though most have weak or mixed evidence:
- Caffeine and green tea extract: Limited short-term weight loss effect (approximately 0.5–1.5 kg). Works by modestly increasing metabolism. No long-term studies.
- Glucomannan (soluble fibre): May cause modest weight loss by increasing fullness. Requires drinking large amounts of water. Risk of choking if not used properly.
- Conjugated linoleic acid (CLA): Minimal effect (approximately 0.5 kg loss). Expensive relative to benefit.
- Garcinia cambogia (hydroxycitric acid): Limited evidence. Most studies show no significant weight loss advantage over placebo.
- Chromium and other minerals: Insufficient evidence for meaningful weight loss in humans.
The NHS and NICE state that most commercial weight loss supplements lack robust clinical trial evidence supporting significant weight loss.
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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 Nutritional Supplements Compare to Prescription Weight Loss Treatment
Unlike unproven supplements, prescription weight loss medications like Mounjaro (tirzepatide) and Wegovy (semaglutide) have undergone rigorous clinical trials. In the STEP trial, semaglutide produced average weight loss of approximately 15% of body weight, whilst most supplements show minimal results. Prescription medications work through established mechanisms—GLP-1 receptor agonists reduce appetite by mimicking natural hormones. Your GP or a prescriber can assess whether prescription weight loss treatment is suitable for you. Calculate your BMI and explore weight loss options using our free BMI calculator and GLP-1 weight loss calculator to compare potential outcomes. For sustainable weight management in the UK, NHS guidance emphasises calorie reduction, physical activity, and behaviour change—often more effective than supplements alone.
- 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.
Are nutritional supplements for weight loss safe?
Most common weight loss supplements are safe when used as directed, but safety depends on the specific product and your individual health. Side effects vary—glucomannan can cause digestive issues or choking if not used properly. Some supplements interact with medications. Always inform your GP of any supplements you're taking, especially if you have health conditions or take prescription medications.
Do weight loss vitamins and supplements actually work?
Evidence for most weight loss supplements is weak or absent. Caffeine and green tea may produce modest effects (under 1 kg loss), but results are inconsistent and smaller than prescription medications or lifestyle changes. The NHS states that commercial weight loss supplements typically lack robust clinical evidence. Sustainable weight loss depends primarily on calorie deficit and physical activity.
What does the NHS say about weight loss supplements?
The NHS recommends focusing on proven weight management methods: reduced-calorie diet, increased physical activity, and behavioural support. Most commercial supplements are not recommended as primary weight loss tools. For significant weight loss support, the NHS offers specialist weight management services and, where eligible, prescription weight loss medications assessed through clinical evaluation.
Can I use supplements alongside prescription weight loss medication?
Some supplements may interact with prescription medications like Mounjaro or Wegovy. Before combining any supplement with prescription weight loss treatment, discuss it with your prescriber or GP. Oral contraceptives, for example, may have reduced effectiveness with certain GLP-1 medications. Always declare all supplements when seeking prescription treatment.
What's the difference between supplements and prescription weight loss medication?
Prescription medications like semaglutide (Wegovy) and tirzepatide (Mounjaro) undergo clinical trials demonstrating significant, consistent weight loss (15–21% body weight). Supplements rarely show similar evidence. Prescription medications require clinical assessment and are available through NHS specialist services or private prescribing. They work through established biological mechanisms, whereas most supplements lack proven effectiveness for meaningful weight loss.
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.