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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4 Week Weight Loss Plan With UK Prescription Medication
A 4 week weight loss plan involving prescription medication can be an effective approach for eligible UK adults. Weight management medications like Mounjaro and Wegovy are now available on the NHS and privately, offering a structured way to support weight loss alongside lifestyle changes. This guide covers which medications are available in the UK, who is eligible, how they work over a 4-week period, and how to access them through either NHS or private routes. Individual results vary, but prescription weight management options can be part of a comprehensive approach to losing weight.
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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 Medications
Three prescription-only medications are currently licensed in the UK for weight management and can form the basis of a structured 4-week weight loss plan:
- Mounjaro (tirzepatide) — A once-weekly injection that activates dual GIP and GLP-1 hormone pathways. Clinical trials showed participants lost an average of 15–21% of body weight over 72 weeks when used alongside a reduced-calorie diet and increased physical activity.
- Wegovy (semaglutide) — A once-weekly GLP-1 injection. In clinical trials, participants lost approximately 14.9% of body weight on average at the maximum dose.
- Saxenda (liraglutide) — A daily GLP-1 injection, a longer-established option in weight management.
All three require a prescription and clinical assessment. Over 4 weeks, you would typically start on a lower dose and potentially escalate, though the full effects of weight loss medication develop over weeks and months rather than within a single month. Use our free GLP-1 weight loss calculator to estimate potential weight loss at different doses.
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 for Weight Loss Medication
NHS access: Available through specialist tier 3 weight management services following a GP referral. Eligibility requires a BMI of 30 or above, or 27–29.9 with weight-related health conditions like type 2 diabetes, high blood pressure, or sleep apnoea. However, NHS waiting lists vary significantly by region — some areas have waiting times of several months or longer.
Private access: Available without NHS referral through GPhC-registered online pharmacies following a clinical assessment by a UK-licensed prescriber. This route offers faster access but involves private costs (typically £129–£320 per month depending on dose). Speak to your GP first to understand your eligibility and explore both options. Our free BMI calculator can help you check whether you may be eligible for prescription weight loss support.
- 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.
What happens in the first 4 weeks of taking Mounjaro or Wegovy?
In week 1–4, you start on a low "starter dose" to allow your body to adjust. Most people do not experience significant weight loss in the first 4 weeks — the medications work by reducing appetite and cravings. You may notice reduced hunger or nausea. Doses are typically escalated every 4 weeks, so week 5 onwards, you move to a higher maintenance dose where weight loss effects become more noticeable.
Can I lose weight in 4 weeks with prescription medication alone?
Prescription weight loss medications work best alongside a reduced-calorie diet and increased physical activity. While some people do experience weight loss in 4 weeks, the average meaningful weight loss typically develops over weeks 8–12 and beyond. Medications are a tool to support your efforts, not a replacement for lifestyle changes.
How do I know if I'm eligible for NHS prescription weight loss treatment?
You are potentially eligible if you have a BMI of 30 or above, or BMI of 27–29.9 with weight-related health conditions (diabetes, high blood pressure, sleep apnoea). Contact your GP to discuss your eligibility. If you meet criteria, you may be referred to a specialist weight management service. Use our free BMI calculator to check your personal BMI.
What's the difference between Mounjaro and Wegovy for a 4-week plan?
Both are once-weekly injections. Mounjaro is a dual GIP+GLP-1 agonist; Wegovy is GLP-1 only. In trials, Mounjaro showed slightly higher average weight loss. However, individual responses vary. Your prescriber will recommend the option most suitable for your health profile.
Can I access prescription weight loss medication privately if NHS waiting lists are long?
Yes. Private online prescribing services can assess you and issue a prescription without NHS referral. This is faster but involves private costs. Many people use both routes — they explore NHS eligibility whilst considering private options to reduce waiting times for treatment to begin.
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.