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
Does Mounjaro Give You Energy or Cause Fatigue?
Mounjaro doesn't directly boost energy, but fatigue is a potential side effect — though it's less common than nausea or digestive changes. Energy levels on Mounjaro vary significantly between individuals. Some people report feeling more energetic as they lose weight and their health improves, whilst others experience temporary fatigue, especially during dose titration. Wegovy users report similar variable experiences. Both are prescription-only GLP-1 and GIP+GLP-1 receptor agonists that work through appetite regulation, not direct energy stimulation. Your personal response depends on your body's adaptation and overall health. Use our free GLP-1 weight loss calculator to understand how these medications may affect your journey.
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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.
How Mounjaro and Wegovy Affect Energy — Clinical Perspective
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist. It doesn't contain stimulants or direct energy-boosting ingredients. Instead, it works by regulating appetite, slowing gastric emptying, and supporting blood sugar control. Fatigue appears in clinical trial data as a less common side effect — the SURMOUNT trials reported tiredness affecting a minority of participants.
Wegovy (semaglutide) operates through GLP-1 pathways only, with a similar side effect profile. Neither medication is designed to increase energy; both are appetite suppressants.
- Why some people feel more energetic: Weight loss itself improves cardiovascular fitness, reduces joint strain, and can enhance sleep quality — all supporting better energy naturally over weeks or months.
- Why some experience fatigue: Rapid calorie deficit, nausea affecting nutrition intake, or individual medication sensitivity can temporarily lower energy during the adjustment period (usually weeks 1–8).
- Dose titration matters: Starting at lower doses (Mounjaro 2.5 mg via KwikPen, Wegovy 0.25 mg) and escalating gradually typically allows your body to adapt, reducing energy dips.
Clinically BackedWeight Loss
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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 Your Energy Needs — Individual Assessment
There is no clinical evidence that Mounjaro provides more or less energy than Wegovy at equivalent dose levels. Both medications carry fatigue as a possible but uncommon side effect. The key difference is mechanism: Mounjaro's dual GIP+GLP-1 action may produce faster weight loss (averaging 15–21% body weight in SURMOUNT trials versus approximately 15% with Wegovy in STEP trials), which could translate to faster energy improvements from weight loss itself — though this is individual.
Your prescriber will assess suitability based on your health profile, existing medications, and medical history — not on energy expectations. If you experience persistent fatigue on either medication, speak to your GP or prescriber; dose adjustment, timing of injections, or dietary support may help. Try our BMI calculator and weight loss projection tool to understand your baseline and potential outcomes with either medication.
- 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.
Does Mounjaro give you energy like a stimulant?
No. Mounjaro is not a stimulant and does not contain caffeine or energy-boosting compounds. It works by regulating appetite and blood sugar. Some users report improved energy over time due to weight loss and health improvements, but this is a secondary effect, not a direct mechanism of the medication.
Is fatigue common on Mounjaro or Wegovy?
Fatigue is listed as a common side effect in clinical trials but affects a minority of users. Most people experience nausea, diarrhoea, or constipation instead. Fatigue is typically temporary during dose titration and often resolves as your body adapts within 2–4 weeks.
Will I feel more energetic after losing weight on Mounjaro?
Many people report improved energy as they lose weight because cardiovascular fitness improves, joint pain decreases, and sleep quality often enhances. These benefits develop gradually over weeks to months, not immediately from starting the medication.
Should I choose Mounjaro or Wegovy based on energy levels?
Energy impact is not a primary factor in choosing between them. Your prescriber will assess suitability based on your BMI, health conditions, medical history, and existing medications. Both require a clinical assessment — discuss energy concerns with your prescriber if you have them.
What should I do if Mounjaro makes me feel fatigued?
Contact your GP or prescriber immediately. Fatigue during dose titration may resolve naturally, but it can also signal dietary deficiency or medication sensitivity. Your prescriber may adjust your dose, timing, or provide nutritional support. Never stop medication without guidance.
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.