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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Using Mounjaro With A Mirena Coil — What You Need To Know
If you're using a Mirena intrauterine device (IUD) and considering Mounjaro for weight management, you'll want to understand how these work together safely. Mounjaro (tirzepatide) is a prescription-only GLP-1 and GIP receptor agonist approved in the UK for weight loss. The Mirena coil is a long-acting reversible contraceptive (LARC) that releases the hormone levonorgestrel directly into your uterus. This guide explains the interaction between the two, what your GP needs to know, and how to access Mounjaro safely if you have a Mirena fitted.
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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.
Mounjaro, The Mirena Coil, And Drug Interactions
The good news: Mounjaro and the Mirena coil can be used together. There is no direct pharmacological interaction between tirzepatide and levonorgestrel — Mounjaro does not reduce the effectiveness of the Mirena or vice versa. However, there are practical considerations your prescriber needs to assess.
Mounjaro may affect the absorption of some oral medications by slowing gastric emptying (how quickly food and tablets move through your stomach). The Mirena coil releases hormones directly into your bloodstream, so this is not affected. However, if you take any oral contraceptives alongside the Mirena — which is unusual but occasionally done — Mounjaro may reduce their absorption, and barrier contraception should be added for 4 weeks after starting and after each dose increase.
More importantly: Mounjaro can cause nausea, vomiting, and abdominal pain, particularly in the first weeks. If you experience severe stomach pain, report it immediately to your GP — it could indicate pancreatitis or other complications, which are rare but serious. The Mirena itself can cause cramping and bleeding changes, so distinguishing between Mirena-related symptoms and Mounjaro side effects is important for your safety.
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.
Accessing Mounjaro With A Mirena: NHS Vs Private Routes
If you're eligible for Mounjaro — typically a BMI of 30 or above, or 27+ with weight-related health conditions — your Mirena coil will not prevent access. Use our free BMI calculator above to check your personal eligibility category.
NHS route: Referral to tier 3 specialist weight management services through your GP. Be honest about your Mirena coil during assessment — this is routine information. NHS availability is variable by region (ICB area) and waiting lists can be several months in many areas.
Private route: Online consultation with a UK-licensed prescriber following a digital assessment. Your medical history — including your Mirena — will be reviewed. If approved, your prescription is dispensed by a GPhC-registered pharmacy. This route typically takes 1–3 days from consultation to first dose. Always disclose your Mirena and all medications during the online assessment form.
- 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.
Will Mounjaro make my Mirena coil less effective at preventing pregnancy?
No. Mounjaro does not reduce the contraceptive effectiveness of the Mirena coil. The Mirena works by releasing the hormone levonorgestrel directly into your uterus, and this is not affected by tirzepatide. However, if you take any oral medications alongside your Mirena, discuss absorption changes with your prescriber.
Can I start Mounjaro if I have a Mirena fitted?
Yes, most people can safely use both. However, your prescriber must know you have a Mirena during your clinical assessment. Both can cause abdominal symptoms (Mirena: cramping; Mounjaro: nausea and stomach pain), so your healthcare provider needs to monitor you carefully to distinguish between them.
What should I tell my GP about my Mirena when requesting Mounjaro?
Tell your GP or prescriber: when your Mirena was fitted, whether you've had any complications (infection, displacement, heavy bleeding), any other medications you take, and any allergies. This information helps them assess whether Mounjaro is safe for you and determine the right starting dose.
Are there any warning signs I should watch for while using both?
Seek medical attention immediately if you experience: severe, persistent stomach pain (possible pancreatitis), serious allergic reaction (swelling of face, lips, or throat), abnormal bleeding or severe cramping different from your usual Mirena experience, or signs of Mirena displacement (sudden loss of strings, severe pain). Contact your GP or NHS 111 if unsure.
Is Mounjaro available on the NHS if I have a Mirena?
Yes, if you meet NHS eligibility criteria (BMI 30+, or 27+ with weight-related health conditions), your Mirena will not prevent NHS prescription. However, access depends on your region's specialist weight management services. Your GP can refer you — waiting times vary from weeks to months.
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.