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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Can You Take Mounjaro Early — Dosing and Comparison
No, you should not take Mounjaro earlier than your scheduled injection day. Mounjaro is a once-weekly GLP-1 and GIP receptor agonist that requires a specific dose titration schedule to allow your body to adjust safely. If you're considering accelerating your treatment because you want faster weight loss results, it's worth understanding how Mounjaro and Wegovy compare in terms of dosing schedules, mechanisms, and what the clinical evidence actually shows about timing and outcomes.
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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.
Mounjaro vs Wegovy — Dosing Timeline and Mechanism Differences
Both Mounjaro and Wegovy are prescription-only weight loss injections, but they work via different mechanisms and follow different dose escalation schedules.
- Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist. It starts at 2.5 mg weekly and escalates every 4 weeks through 5 mg, 7.5 mg, 10 mg, 12.5 mg, and up to 15 mg maximum. The SURMOUNT-1 clinical trial showed average weight loss of approximately 20.9% at the 15 mg dose.
- Wegovy (semaglutide) is a GLP-1-only agonist. It starts at 0.25 mg and escalates over 16 weeks to a maximum of 2.4 mg. The STEP-1 trial showed average weight loss of approximately 14.9% at the maximum dose.
The dose titration schedules exist for a reason: they allow your body to adjust to the medication, minimise nausea and gastrointestinal side effects, and ensure the medication works safely for you. Skipping doses or taking Mounjaro earlier than scheduled could reduce its effectiveness and increase side effect risk.
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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.
Why Your Prescriber Sets Your Mounjaro Schedule
Your prescriber determines your Mounjaro dosing timeline based on your individual health profile, BMI, and any weight-related conditions you have. The 4-week intervals between dose increases are evidence-based—they give your body time to adapt to each dose level before escalation.
If you're experiencing slower-than-expected weight loss on your current Mounjaro dose, contact your prescriber rather than adjusting your schedule independently. They can assess whether increasing to the next dose is appropriate, whether lifestyle factors need adjustment, or whether your individual response simply requires more time. Taking Mounjaro early or at shorter intervals without clinical guidance is not recommended and could affect your safety and results.
- 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 if I take Mounjaro before my scheduled injection day?
Taking Mounjaro earlier than scheduled is not recommended. The 7-day weekly schedule is designed for safety and effectiveness. If you accidentally inject early (within 72 hours of your last dose), contact your prescriber or pharmacist for guidance. Never take a double dose to compensate.
Can I switch from Wegovy to Mounjaro early if I want faster results?
Switching between GLP-1 medications should only be done under prescriber guidance. While Mounjaro's dual mechanism may produce slightly faster average weight loss in trials, individual results vary significantly. Switching requires a clinical assessment and proper dose planning—it's not a shortcut to faster outcomes.
How long does it take to reach maximum Mounjaro dose?
Starting from 2.5 mg, reaching the maximum 15 mg dose typically takes approximately 20–21 weeks (five 4-week escalation intervals). Some people reach their effective dose earlier at 5 mg, 7.5 mg, or 10 mg and may not need to escalate further.
What if my Mounjaro isn't working fast enough?
Weight loss is a gradual process. If you're not seeing expected results after at least 12 weeks on your current dose, discuss this with your prescriber. They may recommend dose escalation, lifestyle assessment, or investigation of other factors. Use our free GLP-1 weight loss calculator to understand realistic timelines for different doses.
Does taking Mounjaro more frequently increase weight loss?
No. Taking Mounjaro more frequently than once weekly is not approved and could be unsafe. Weight loss injections work most effectively when combined with a reduced-calorie diet and increased physical activity—medication alone isn't the solution. Your prescriber can advise on the full approach.
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.