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
Mounjaro and Tiredness: UK Access and Cost Guide
Tiredness (fatigue) is a commonly reported side effect when starting Mounjaro (tirzepatide), though it typically improves as your body adjusts. This guide explains what causes Mounjaro-related fatigue, how to access Mounjaro in the UK through both NHS and private routes, and what you can expect to pay. Whether you're considering prescription weight loss treatment or already taking a GLP-1 injection, understanding both the side effects and costs helps you make informed decisions about your health.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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.
Mounjaro Tiredness: Why It Happens and What to Expect
Tiredness is listed as a common side effect of Mounjaro, affecting up to 1 in 10 people during treatment. This fatigue typically occurs because your body is adjusting to the tirzepatide dose, experiencing reduced calorie intake, and adapting to changes in appetite regulation. When you first start Mounjaro or increase your dose, your energy levels may dip for several days.
- Fatigue often improves within 1–2 weeks as your body adapts
- Staying hydrated and eating regular balanced meals helps combat tiredness
- Insufficient sleep or high stress can worsen fatigue
- Some people experience persistent tiredness — discuss this with your prescriber if it continues beyond 2 weeks
Tiredness is different from more serious side effects like severe stomach pain (possible pancreatitis) or gallbladder issues, which require urgent medical attention. Use our free GLP-1 weight loss calculator to understand how Mounjaro works and what to expect during dose titration, the gradual weekly increases that help your body adjust.
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.
How to Access Mounjaro in the UK: NHS vs Private Cost
In the UK, Mounjaro (tirzepatide) is available through two routes: NHS specialist weight management services and private prescribing. NHS access requires referral to a tier 3 or tier 4 specialist weight management service — not standard GP prescription. Waiting lists vary significantly by region, often extending several months. Private access is available through GPhC-registered online prescribers following a clinical consultation. Private costs typically range from £129–£320 per month depending on your dose and the provider. A Mounjaro KwikPen contains 4 weekly injections. Many people choose private prescribing for faster access, though NHS access remains available for those meeting eligibility criteria. Your prescriber will assess whether Mounjaro suits your health profile before issuing a prescription.
- 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.
Why does Mounjaro cause tiredness?
Tiredness occurs as your body adapts to tirzepatide, particularly during dose titration. Lower food intake, metabolic changes, and your system adjusting to appetite regulation can all contribute to fatigue. This side effect usually improves within 1–2 weeks.
How much does Mounjaro cost privately in the UK?
Private Mounjaro typically costs £129–£320 per month depending on your dose (from 2.5 mg to 15 mg) and provider. Each KwikPen contains 4 weekly injections. Costs vary between prescribing services, so comparing options is worthwhile.
Can I get Mounjaro on the NHS in the UK?
Yes, Mounjaro is available through NHS specialist weight management services (tier 3/4). However, access requires GP referral and assessment. Availability varies by region, and waiting lists can be lengthy. Private prescribing offers faster access without NHS referral.
How is a Mounjaro prescription issued online?
You complete an online health questionnaire with a UK-licensed prescriber, who reviews your medical history and eligibility. If appropriate, they issue a prescription dispensed by a GPhC-registered pharmacy. The entire process typically takes 1–2 working days.
Is tirzepatide the same as Mounjaro?
Yes — tirzepatide is the active ingredient in Mounjaro. Mounjaro is the brand name. Tirzepatide is a dual GIP and GLP-1 receptor agonist, which differs from Wegovy (semaglutide), a GLP-1-only injection. Both are licensed for UK weight management.
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.