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 6 Weeks — UK Prescription Medication Options
Losing weight in 6 weeks is possible with the right approach, particularly when combining lifestyle changes with prescription weight management medication. The UK has several licensed prescription weight loss options available through NHS specialist services or private online prescribing. While the NHS recommends losing weight at a sustainable rate of 0.5 to 1 kg per week, prescription medications like GLP-1 weight loss injections may help eligible adults achieve greater results alongside diet and physical activity. This guide covers your options, eligibility criteria, and how to get started.
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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 Loss Medication
Three prescription weight loss medications are currently licensed in the UK for weight management in eligible adults:
- Mounjaro (tirzepatide) — A dual GIP and GLP-1 receptor agonist administered once weekly. Clinical trials showed users lost an average of 15–21% of body weight over 72 weeks when combined with a reduced-calorie diet and physical activity.
- Wegovy (semaglutide) — A GLP-1 receptor agonist injected once weekly. Clinical trials demonstrated average weight loss of approximately 15% body weight over 68 weeks.
- Saxenda (liraglutide) — A daily GLP-1 injection with similar mechanisms to Wegovy. Average weight loss is typically 5–10% of body weight.
All three medications work by regulating appetite and helping you feel fuller after smaller meals. Individual results vary significantly and depend on your starting weight, metabolism, adherence to lifestyle changes, and which dose you're on. For weight loss in 6 weeks specifically, early results may include 2–4 kg loss on average, though this varies considerably between individuals.
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 Access vs Private Prescribing
NHS access: Prescription weight loss medications are available through tier 3 specialist weight management services, but you must be referred by your GP. Eligibility typically requires a BMI of 30 or above, or 27 or above with weight-related health conditions like type 2 diabetes or high blood pressure. However, NHS waiting lists can be lengthy — sometimes months or years depending on your region.
Private prescribing: GLP-1 weight loss injections are available through GPhC-registered online pharmacies following an online clinical assessment with a UK-licensed prescriber. This route offers faster access without NHS referral, though costs range from approximately £129–£320 monthly depending on dose. Either route requires a clinical assessment to confirm the medication is appropriate for you.
- 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.
Can I lose weight in 6 weeks with prescription medication?
Prescription weight loss injections may help, but results vary. The NHS recommends losing 0.5–1 kg weekly for sustainable results — so in 6 weeks you might expect 3–6 kg loss with medication and lifestyle changes combined. Clinical trials show greater loss is possible, but individual results depend on starting weight, the specific medication, dose, and your adherence to diet and exercise changes. Use our free GLP-1 weight loss calculator to estimate potential results at different doses.
Who is eligible for prescription weight loss medication in the UK?
You may be eligible if you have 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. For South Asian, Chinese, Black African, or Black Caribbean adults, lower BMI thresholds apply. Eligibility is assessed individually by a prescriber — your GP can refer you to NHS specialist services, or you can access private prescribing following an online clinical assessment.
What's the difference between Mounjaro and Wegovy?
Mounjaro (tirzepatide) activates two hormone pathways (GIP and GLP-1), whilst Wegovy (semaglutide) activates only GLP-1. Clinical trials suggest Mounjaro may produce slightly greater average weight loss (15–21% vs 15%), but both are effective. Wegovy has been available longer in the UK. Both are once-weekly injections. The choice depends on your individual health profile, which a prescriber will assess.
How long does it take to see results from weight loss medication?
Many people notice reduced appetite within 1–2 weeks of starting. Measurable weight loss typically becomes apparent after 4–6 weeks, though this varies. Your body continues to adjust as the dose increases — most medications are gradually stepped up over 16–20 weeks to reach the maximum effective dose. Track your progress over weeks rather than days using our free progress tracker.
Can I get weight loss injections on the NHS quickly?
NHS access is through tier 3 specialist weight management services following a GP referral. Waiting times vary significantly by region — some areas have waits of several months or longer due to demand. Private prescribing offers faster access (typically within 1–2 weeks) through online clinical assessment, though costs are higher. Ask your GP about NHS availability in your area and whether private prescribing might be an option for you.
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.