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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Weight Loss in Week 3: UK Prescription Medication Options
By week 3 of your weight loss journey, many people are wondering whether prescription medication might help accelerate their progress. In the UK, several licensed options are available for eligible adults, alongside diet and exercise. This guide explores the prescription weight loss medications available through the NHS and private prescribing, who qualifies, and how to take the next step. Whether you're considering GLP-1 weight loss injections or want to understand your options, we'll help you make an informed decision about weight management in the UK.
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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 Available in Week 3
Three prescription-only medications are licensed in the UK for weight management: Mounjaro (tirzepatide), a dual GIP and GLP-1 receptor agonist; Wegovy (semaglutide), a GLP-1 receptor agonist; and Saxenda (liraglutide), also a GLP-1 receptor agonist. All are injectable medications given once weekly (or daily for Saxenda). In clinical trials, these medications helped participants lose an average of 15–21% of their body weight when combined with a reduced-calorie diet and increased physical activity.
To be eligible for prescription weight loss medication in the UK, you typically need a BMI of 30 or above, or 27 or above with weight-related health conditions such as type 2 diabetes, high blood pressure, or cardiovascular disease. Adults from South Asian, Chinese, Black African, or Black Caribbean backgrounds may qualify at lower BMI thresholds due to higher health risks at lower weights.
Calculate your BMI using our free BMI calculator above to see where you stand. Individual results vary significantly, and medication is always prescribed alongside lifestyle changes, not instead of them.
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.
NHS vs Private Access: How to Find Out If You're Eligible
NHS route: Referral to a specialist tier 3 weight management service through your GP is the NHS pathway. However, availability varies significantly by region, and waiting lists can be lengthy. Contact your GP to discuss whether referral is appropriate for you and what timescales your local integrated care board (ICB) is currently managing.
Private route: GPhC-registered online pharmacies offer prescription weight loss medication following an online clinical assessment with a UK-licensed prescriber. This route is faster and doesn't require NHS referral. Use our free GLP-1 weight loss calculator to estimate potential progress at different doses. Your prescriber will assess suitability based on your health history, medications, and weight loss goals.
Either way, having an honest conversation with your GP about your weight loss goals is always recommended, especially if you're taking other medications.
- 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 prescription weight loss medication available on the NHS in week 3 of my weight loss journey?
Yes, if you meet eligibility criteria. NHS access is through specialist weight management services (tier 3), typically accessed via GP referral. Availability and waiting times vary by region. Your GP can advise whether referral is appropriate and give you realistic timescales for your area.
What's the difference between Mounjaro and Wegovy for weight loss?
Both are once-weekly injections licensed for weight management in the UK. Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist, while Wegovy (semaglutide) is a GLP-1 agonist only. Clinical trials showed Mounjaro may produce slightly higher average weight loss (~21% vs ~15%), but results vary individually. Your prescriber will recommend the most suitable option based on your health profile.
Can I get weight loss medication privately without waiting for the NHS?
Yes. Private online prescribing services offer faster access following an online clinical assessment. You'll need to meet eligibility criteria (BMI ≥30, or ≥27 with weight-related health conditions) and provide health details. Costs vary by provider and dose, typically ranging from £130–£320 monthly.
What should I tell my GP about considering weight loss medication?
Be honest about your weight loss goals, any previous attempts, and your current diet and exercise routine. Mention any health conditions, medications you're taking, and whether you have a family history of thyroid or pancreatic issues. Your GP can assess whether medication is appropriate and discuss side effects, interactions, and monitoring requirements.
Will weight loss medication work without diet and exercise changes?
No. Prescription weight loss medications are designed to work alongside a reduced-calorie diet and increased physical activity. Medications help reduce appetite and support feeling fuller, but sustainable weight loss requires lifestyle changes. Use our free progress tracker to log both medication use and lifestyle changes alongside your weight loss journey.
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.