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
Can You Use Mounjaro With A Mirena Coil?
If you're using a Mirena coil for contraception and considering Mounjaro (tirzepatide) for weight management, you may have questions about whether these two can be used together safely. The good news is that the Mirena coil and Mounjaro can generally be used at the same time, as Mounjaro does not interact with the Mirena's hormonal mechanism. However, there are important contraceptive and health considerations you should discuss with your GP or prescriber before starting tirzepatide.
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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.
How Mounjaro And The Mirena Coil Work
Mounjaro (tirzepatide) is a dual GLP-1 and GIP receptor agonist prescription-only weight management injection licensed in the UK. It works by regulating appetite hormones and helping you feel fuller after eating. It does not interfere with how hormonal contraception functions.
The Mirena coil releases a small amount of the hormone levonorgestrel directly into your uterus to prevent pregnancy. Because the Mirena works locally in the uterus and Mounjaro works systemically (throughout the body) via appetite hormone pathways, there is no direct interaction between them.
However, Mounjaro may affect how your body absorbs other oral medications — it slows gastric emptying, meaning food and medications stay in your stomach longer. This is why it's essential to inform your prescriber about all medications and contraception you're using, including the Mirena coil, before starting tirzepatide.
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.
Important Contraceptive And Absorption Considerations
The Mirena coil is not affected by Mounjaro because it releases hormones directly into the uterus, bypassing the digestive system. However, if you take any oral medications alongside Mounjaro — including certain antibiotics or other drugs — absorption may be delayed or reduced.
For your safety, your prescriber will ask about your complete contraceptive history and all current medications before issuing a Mounjaro prescription. This is standard practice and ensures the prescription is appropriate for you. Always mention you have a Mirena coil during your clinical assessment. If you experience any unusual symptoms after starting Mounjaro — such as changes in your menstrual cycle or unexpected side effects — contact your GP promptly for advice.
- 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 interact with the Mirena coil?
No. Mounjaro and the Mirena coil can be used together safely. The Mirena releases hormones locally into the uterus, while Mounjaro works via systemic appetite hormone pathways. There is no direct interaction between them.
Will Mounjaro affect my Mirena's effectiveness?
The Mirena coil's effectiveness is not affected by Mounjaro tirzepatide. The coil works independently of the digestive system, so Mounjaro's effects on medication absorption do not impact contraceptive efficacy.
Do I need to tell my prescriber I have a Mirena coil?
Yes. Always inform your GP or prescriber about all contraception, medications, and medical devices you use before starting Mounjaro. This helps them assess whether the prescription is suitable for you and identify any potential issues.
What should I do if I notice changes in my menstrual cycle after starting Mounjaro?
Contact your GP. While the Mirena itself may cause lighter or absent periods, starting a new medication can sometimes trigger unexpected changes. Your GP can investigate and advise whether to continue Mounjaro or adjust your healthcare plan.
Can I use Mounjaro if I'm planning to have the Mirena removed?
Yes. You can start or continue Mounjaro whether your Mirena is in place or after removal. Discuss the timing with your GP to ensure safe management of both contraception and weight management alongside tirzepatide.
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.