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
Taking Mounjaro Twice A Week — What You Need to Know
Mounjaro is designed as a once-weekly injection, not twice-weekly. If you're considering a different dosing schedule, it's important to understand how tirzepatide actually works and how it compares to alternatives like Wegovy. This guide explains the standard UK dosing for Mounjaro, why the once-weekly schedule is prescribed, and what to discuss with your prescriber if you have concerns about your current treatment plan.
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.
Standard Mounjaro Dosing vs Wegovy — How They Compare
Mounjaro (tirzepatide) is always prescribed as a once-weekly injection — there is no twice-weekly dosing option. The medication comes in pre-filled KwikPens containing four weekly doses, with your prescriber gradually increasing the dose every 4 weeks, from 2.5 mg up to a maximum of 15 mg per week.
Wegovy (semaglutide), another GLP-1 weight loss injection licensed in the UK, is also once-weekly. Unlike Mounjaro, Wegovy uses a different mechanism — it's a single GLP-1 receptor agonist, whereas Mounjaro is a dual GIP and GLP-1 receptor agonist. Clinical trial data from SURMOUNT-1 (Mounjaro) showed average weight loss of approximately 15–21% body weight at maximum dose, while STEP-1 trials (Wegovy) showed approximately 15% at the same timepoint. Both require clinical assessment and are prescription-only in the UK.
If you're thinking about twice-weekly dosing or adjusting your schedule, this is a conversation to have with your GP or prescriber — they can assess whether your current dose is working for you and discuss adjustments within the licensed protocol.
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.
Why Mounjaro Is Once-Weekly and What That Means for You
Mounjaro's once-weekly schedule is based on how the medication works in your body. Tirzepatide has a long half-life, meaning it stays active in your system for several days after injection. Taking it twice weekly would mean overlapping doses and unpredictable blood levels — this isn't how the medication was designed or tested.
If your current once-weekly Mounjaro dose isn't giving you the results you'd hoped for, your prescriber has several options: they can increase your dose (up to 15 mg maximum), or consider whether a different medication might be more suitable. This is why using our free GLP-1 weight loss calculator can help you understand projected weight loss ranges at different doses, and our BMI calculator helps track how your weight relates to health guidelines — both tools support conversations with your prescriber about whether your current treatment plan is working for you.
- 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.
Can I take Mounjaro twice a week instead of once a week?
No. Mounjaro is only prescribed as a once-weekly injection. There is no licensed twice-weekly dosing schedule. If you feel your current dose isn't effective, discuss dose escalation or alternative medications with your prescriber rather than changing the injection frequency on your own.
How does Mounjaro's once-weekly injection compare to Wegovy?
Both Mounjaro and Wegovy are once-weekly injections licensed for weight management in the UK. The key difference is mechanism: Mounjaro is a dual GIP+GLP-1 agonist, while Wegovy is GLP-1-only. Clinical trials showed similar average weight loss percentages, though individual results vary significantly.
What if I've missed a Mounjaro injection — can I take two the next week?
No. If you miss a dose within 4 days, inject as soon as you remember and continue your normal schedule. If it's been more than 4 days, skip that dose and take your next injection on the normal day. Never double-dose.
Why is Mounjaro given weekly instead of daily like some diabetes medicines?
Tirzepatide has a longer half-life than many other GLP-1 medications, meaning it remains active in your body for several days. This allows for once-weekly dosing, which is more convenient and was how the medication was studied in clinical trials.
What should I discuss with my GP if I'm not seeing weight loss on Mounjaro?
Talk to your prescriber about dose escalation (doses increase every 4 weeks up to 15 mg), whether you're combining it with dietary changes and activity, and whether Mounjaro remains the best choice for you. They may also consider your overall health and adjust your treatment plan accordingly.
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.