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
Free tracker included with every download this week
When Will I Notice Weight Loss on UK Medications?
When taking prescription weight management medication in the UK, you may start noticing physical changes within 2–4 weeks, though significant weight loss typically becomes visible after 8–12 weeks. The timeline depends on the medication type, your dose, starting weight, and how your body responds. Most UK adults using GLP-1 medications like Wegovy or dual GIP/GLP-1 medications like Mounjaro see measurable results within the first month, but individual results vary considerably. This guide explains realistic timelines for prescription weight loss medication available through NHS specialist services and private prescribing 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 and Timeline Expectations
Mounjaro (tirzepatide) is a once-weekly dual GIP/GLP-1 injection. Clinical trials showed average weight loss of 15–21% body weight over 72 weeks, with noticeable appetite reduction often within 2–3 weeks of starting. Physical weight loss typically becomes visible after 4–6 weeks.
Wegovy (semaglutide) is a once-weekly GLP-1 injection. Trial data showed approximately 15% average weight loss, with appetite suppression often felt within days to weeks, but visible weight loss usually within 6–8 weeks.
Saxenda (liraglutide) is a daily GLP-1 injection; timelines are similar but results are typically slightly more gradual than weekly injections.
All three are prescription-only and require a clinical assessment. Access through NHS weight management services varies by region — waiting times can extend months. Private prescribing offers faster access following an online clinical assessment. Your GP can advise you on NHS eligibility and local specialist referral options.
To check your current BMI and understand your baseline for weight loss, use our free BMI calculator above.
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 and Realistic Timelines
On the NHS route, you will be referred to a specialist tier 3 weight management service by your GP if eligible. Assessment, prescription, and monitoring happen through this service. Eligibility requires a BMI of 30 or above, or 27–29.9 with weight-related health conditions like type 2 diabetes or high blood pressure. NHS access is free but availability and waiting lists vary significantly across England, Scotland, Wales, and Northern Ireland.
On the private route, a UK-licensed prescriber offers an online consultation and issues a prescription if clinically appropriate. Private prescribing is faster (days rather than months) and does not require NHS referral, but carries a cost. Track your weight loss progress using our free progress tracker to monitor results month-to-month, regardless of which access route you choose.
Realistic expectations: expect appetite reduction within days to weeks, visible weight loss within 4–8 weeks, and significant cumulative results over 3–6 months when combined with a reduced-calorie diet and increased physical activity.
- 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.
How quickly will I lose weight on Mounjaro or Wegovy?
Individual results vary significantly. Appetite suppression often occurs within days to weeks, but visible weight loss typically becomes noticeable after 4–8 weeks. Clinical trials showed average weight loss of 15–21% (Mounjaro) and 15% (Wegovy) over 72 weeks. Results depend on your starting weight, dose, diet, exercise, and individual metabolism. Your prescriber can discuss realistic timelines for you.
Will I notice weight loss in the first week?
Most people feel appetite reduction within the first week or two, particularly reduced cravings and feeling fuller after smaller meals. However, visible weight loss (measurable on scales or visible in clothes) usually takes 3–4 weeks minimum. Rapid early weight loss may include water loss rather than fat loss. The NHS recommends sustainable loss of 0.5–1 kg per week.
What if I don't notice weight loss after a month?
If you have not seen measurable weight loss after 4–6 weeks, discuss this with your prescriber. Possible reasons include insufficient dose escalation, not maintaining a calorie deficit, metabolic factors, or the medication not being suitable for you. Your prescriber may adjust your dose or review your diet and activity levels. Never stop medication without professional guidance.
Can I use our GLP-1 weight loss calculator to predict my timeline?
Yes. Our free weight loss calculator can help you estimate potential weight loss at different doses based on clinical trial data. Enter your current weight and height to see projected results over time. Remember that these are averages — your individual timeline may differ. Combine this with our BMI calculator to track your progress from baseline to target BMI.
What's the difference between NHS and private timelines?
NHS timeline: GP referral (weeks 1–4), waiting list (weeks to months), specialist assessment, then prescription initiation — total 3–12 months depending on your region. Private timeline: online consultation (days), prescription issued, medication dispatched — total days to weeks. Results timelines are similar once medication is started; access route just affects how quickly you begin treatment.
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.