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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Spirulina Weight Loss — What UK Adults Need to Know
Spirulina is a blue-green algae supplement popular for general health, but it is not a weight loss medication. If you're looking for evidence-based weight management support in the UK, prescription options like Mounjaro and Wegovy are available through the NHS or private prescribing. These GLP-1 medications have been clinically proven to support weight loss when used alongside a reduced-calorie diet and increased physical activity. This guide explains what prescription weight management options are available to eligible UK adults and how to access them.
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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 Prescription Weight Management Options
If you're interested in weight management medication in the UK, three prescription options are currently licensed for adults:
- Mounjaro (tirzepatide) — a dual GIP and GLP-1 receptor agonist given as a once-weekly injection. Clinical trials showed an average weight loss of 15–21% of body weight over 72 weeks.
- Wegovy (semaglutide) — a GLP-1 receptor agonist given once weekly. In clinical trials, participants lost an average of approximately 15% of their body weight at the maximum dose.
- Saxenda (liraglutide) — a GLP-1 receptor agonist given as a daily injection. Less commonly prescribed but available through private providers.
To be eligible, you typically need a BMI of 30 or above, or 27 or above with a weight-related health condition such as type 2 diabetes, high blood pressure, or sleep apnoea. Individual results vary significantly. These medications work best alongside dietary changes and increased physical activity, not as standalone treatments. Calculate your BMI using our free BMI calculator above to check where you stand.
Clinically BackedWeight 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 to Access Weight Loss Medication in the UK
NHS access: You can ask your GP for a referral to a specialist tier 3 weight management service. NHS funding and availability vary significantly by region, and waiting lists can be lengthy.
Private access: Weight loss medications are available through registered online prescribers following a clinical assessment. This route does not require an NHS referral and is often faster.
Whichever route you choose, a licensed prescriber will assess your individual health, medical history, and eligibility before issuing a prescription. Start by speaking with your GP about your weight management goals — they can advise on both NHS and private options available in your area. Use our free GLP-1 weight loss calculator to get an estimate of potential weight loss if you are prescribed medication.
- 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.
Is spirulina effective for weight loss?
Spirulina is a nutrient-rich algae supplement that may support general health, but there is limited clinical evidence that it causes meaningful weight loss on its own. It is not a weight loss medication. If you want evidence-based weight loss support, prescription GLP-1 medications like Mounjaro or Wegovy have strong clinical trial data.
What's the difference between a supplement and a weight loss medication?
Supplements like spirulina are food products with minimal regulatory oversight. Weight loss medications like Mounjaro and Wegovy are prescription-only medicines tested in rigorous clinical trials, approved by the MHRA, and require a clinical assessment before prescription. Medications have proven weight loss efficacy; supplements do not.
Can I get weight loss medication on the NHS?
Yes. If you meet eligibility criteria (typically BMI 30+, or 27+ with weight-related health conditions), you can ask your GP for a referral to a specialist weight management service. Availability and waiting times vary by region. Private options are also available without an NHS referral.
How much weight can I lose with prescription weight loss medication?
In clinical trials, Mounjaro users lost an average of 15–21% of body weight, and Wegovy users lost approximately 15%. However, individual results vary significantly based on genetics, lifestyle, and adherence. Weight loss medication works best alongside a reduced-calorie diet and increased physical activity.
Do I need a prescription for spirulina?
No. Spirulina is an over-the-counter supplement available in health food shops and online. You do not need a prescription. However, if you want prescription weight loss medication, you will need a clinical assessment from a licensed prescriber—either through your GP or a private online service.
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.