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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Mounjaro Sleep Side Effects vs Wegovy
Sleep disturbances can occur with both Mounjaro (tirzepatide) and Wegovy (semaglutide), though they're not among the most common side effects reported in clinical trials. Both are prescription-only GLP-1-based weight management injections used in the UK, but they work slightly differently — which may affect how individuals experience sleep-related side effects. Understanding the differences can help you have a more informed conversation with your GP or prescriber about which medication might be more suitable for your situation.
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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.
How Mounjaro and Wegovy Differ in Mechanism
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two separate hormone pathways simultaneously. This dual mechanism may produce different metabolic effects compared to single-pathway medications, potentially affecting sleep in different ways.
Wegovy (semaglutide) is a GLP-1 receptor agonist only, activating one hormone pathway. This single mechanism has been studied extensively in the STEP clinical trials, with published data on side effect frequency.
In Mounjaro's SURMOUNT-1 trial, insomnia and sleep-related side effects were reported by a small percentage of participants. Similarly, in Wegovy's STEP trials, sleep disturbances were uncommon but documented. Neither medication lists sleep problems as a "very common" side effect (affecting more than 1 in 10 people). Individual responses vary considerably, and factors like dose titration, gastrointestinal symptoms (which can disturb sleep), and personal health history all influence sleep quality during treatment.
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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.
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Which Medication Might Suit You Better?
Choosing between Mounjaro and Wegovy is not based on minor side effect differences — it's a clinical decision made by your prescriber based on your full health picture, including your BMI, weight-related health conditions, other medications, and personal tolerance. Both medications require a prescription and clinical assessment before you can begin treatment.
If you're concerned about sleep disturbance, mention this to your prescriber before starting either medication. You can also use our free GLP-1 weight loss calculator to understand the expected outcomes at different doses, and our BMI calculator to check your starting point — these may help you discuss realistic expectations with your GP or clinic. Sleep issues may also improve as your body adjusts to the medication, or if gastrointestinal side effects (which can disrupt sleep) settle during dose titration.
- 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.
Is insomnia a common side effect of Mounjaro?
No. In clinical trials, insomnia and sleep disturbances were uncommon with Mounjaro (tirzepatide). They were not listed as "very common" side effects. Individual experiences vary, and sleep quality may be affected indirectly by gastrointestinal symptoms, which typically improve as your body adjusts during dose titration.
Does Wegovy cause sleep problems?
Sleep disturbances are not a common side effect of Wegovy (semaglutide) in clinical trials. However, some individuals may experience changes to sleep patterns, often related to nausea or stomach discomfort rather than the medication directly. These symptoms typically improve after the first few weeks.
How do I know which medication is better for sleep?
Neither medication is specifically "better" for sleep based on clinical data. Your prescriber will recommend the most suitable option based on your full health history, not minor side effect differences. Discuss any sleep concerns when you have your clinical assessment — your prescriber can help you weigh the pros and cons for your individual situation.
Can gastrointestinal side effects affect my sleep with Mounjaro or Wegovy?
Yes. Both medications can cause nausea, vomiting, constipation, or diarrhoea, especially during the first few weeks and during dose titration. These symptoms may indirectly disturb sleep. They typically improve significantly after 2–4 weeks as your body adjusts. Staying hydrated and eating smaller, lighter meals can help.
What should I tell my GP about sleep before starting either medication?
Mention if you have a history of sleep disorders, sleep apnoea, or shift work. Also report if you're taking any medications that affect sleep. Your GP can then assess whether either Mounjaro or Wegovy is appropriate and may offer advice on managing sleep during the initial adjustment period.
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