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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How Long Do Mounjaro Side Effects Last?
Mounjaro side effects typically peak during the first 4–8 weeks of treatment, then gradually improve as your body adjusts to the tirzepatide injection. Most common side effects like nausea and stomach discomfort tend to resolve within 2–4 weeks, though some people experience them longer. Unlike a one-off medication, Mounjaro's side effects are tied to dose changes — when you increase your kwikpen dose, symptoms may temporarily return. This guide compares how Mounjaro and Wegovy side effect timelines differ and what the clinical trials revealed about duration.
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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: Side Effect Duration & Clinical Evidence
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, while Wegovy (semaglutide) is a GLP-1 agonist only — this mechanism difference affects how side effects develop and resolve.
- Mounjaro side effects: Nausea and GI symptoms peak around weeks 2–4 after starting or dose escalation, typically subsiding by week 6–8 as your body adapts. The SURMOUNT-1 trial showed most participants experienced symptom improvement by their second or third month. Hair loss (alopecia) can persist longer — sometimes weeks 8–12+ into treatment.
- Wegovy side effects: The STEP trials showed similar timelines — nausea and vomiting peak in weeks 1–3, usually resolve by week 5–8. Because Wegovy doses are smaller and escalate more gradually (0.25 mg → 2.4 mg over 16 weeks), the transition between doses causes less dramatic symptom spikes than Mounjaro's larger dose increments (2.5 mg → 15 mg).
- Key difference: Mounjaro's faster escalation can mean side effects recur with each dose increase, whereas Wegovy's slower titration may result in fewer acute symptom flares.
Individual responses vary significantly — some people experience minimal side effects, whilst others require 8–12 weeks for symptoms to fully resolve.
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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.
Which Medication Suits You? Prescriber Assessment & Duration
Neither Mounjaro nor Wegovy is objectively "better" for side effect duration — it depends on your personal tolerance and health profile. A UK-licensed prescriber will assess which medication suits you based on your medical history, other medications, and preferences. Both are prescription-only and require a clinical assessment before being prescribed.
- Nausea management: Most UK healthcare professionals recommend eating small, frequent meals and staying hydrated during the adjustment period. Anti-nausea strategies don't shorten symptom duration but improve daily functioning whilst you wait for adaptation.
- Dose adjustment: If side effects are severe, your prescriber may delay dose escalation, allowing your body more time to adapt before advancing to the next tier.
- Monitoring: Track your symptoms using our free progress tracker to identify patterns and share with your prescriber — this helps guide personalised dose timing.
Most people find that after 8–12 weeks on a stable dose, side effects are minimal, and appetite suppression (the therapeutic benefit) becomes the dominant experience.
- 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 long does nausea from Mounjaro last?
Nausea typically peaks in the first 2–4 weeks after starting Mounjaro or increasing your dose, and usually improves significantly by week 6–8. However, individual timelines vary — some people experience mild nausea for 10–12 weeks, whilst others adapt within 3 weeks. If nausea persists beyond 8 weeks at a stable dose, inform your GP or prescriber.
Are Mounjaro and Wegovy side effect durations the same?
Both medications have similar side effect timelines — nausea and GI symptoms typically peak around weeks 2–4 and resolve by weeks 6–8. However, Wegovy's slower dose escalation (smaller increments over 16 weeks) may result in fewer acute symptom flares compared to Mounjaro's faster titration schedule. Individual responses vary significantly regardless of which medication.
What should I do if side effects don't improve after 8 weeks?
Contact your GP or prescriber. Persistent side effects after 8 weeks on a stable dose aren't typical. Your prescriber may adjust your dose, recommend anti-nausea strategies, or reassess whether the medication is suitable for you. Do not stop taking Mounjaro without professional guidance.
Will side effects return when I increase my Mounjaro dose?
Yes, side effects often temporarily return when you escalate to a higher dose of Mounjaro. This is normal and usually temporary — most people readjust within 1–2 weeks of the dose increase. Your prescriber will schedule dose increases at least 4 weeks apart to allow adjustment time between escalations.
Can I prevent Mounjaro side effects during the adjustment period?
You cannot prevent side effects, but you can manage them. Small, frequent meals; staying hydrated; avoiding fatty or spicy foods; and ginger or anti-nausea strategies help many people. Use our free BMI calculator and weight loss calculator to track your health progress alongside symptom management, keeping records to share with your prescriber.
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.