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 Affect The Coil?
If you're using a contraceptive coil (intrauterine device or IUD) and considering Mounjaro, you're right to ask about potential interactions. The good news is that Mounjaro (tirzepatide) does not directly interfere with how the coil works. However, there are important considerations about how Mounjaro may affect other medications and hormonal contraceptives that you should discuss with your GP or prescriber before starting treatment.
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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 Works and Contraceptive Considerations
Mounjaro is a prescription-only injection that works as a dual GIP and GLP-1 receptor agonist to support weight management. The contraceptive coil (copper IUD or hormonal IUD like Mirena) is not affected by the way Mounjaro works in your body—tirzepatide does not reduce the coil's effectiveness.
However, a crucial point: Mounjaro may reduce how your body absorbs oral medications, including oral contraceptive pills. The tirzepatide slows gastric emptying (how quickly food leaves your stomach), which can affect the absorption of tablets taken by mouth. This is why your prescriber will ask about all medications and contraceptives you're using.
- Non-oral contraceptives (coils, implants, injections) are not affected
- Oral contraceptive pills may have reduced absorption
- Your prescriber must assess your individual situation
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.
What You Need to Tell Your Prescriber
Before starting Mounjaro, inform your prescriber that you're using a contraceptive coil. While the coil itself will continue to work, your prescriber needs to know your complete contraception and medication history to ensure there are no interactions.
If you're also taking any oral medications alongside your coil (including oral contraceptive pills, blood pressure tablets, or other treatments), mention these too. Your prescriber may recommend additional barrier contraception or discuss switching to a non-oral contraceptive if you're taking multiple oral medications. Always follow your prescriber's specific guidance—eligibility and suitability for Mounjaro is assessed individually.
Q1: Does Mounjaro make the coil less effective? A1: No. The contraceptive coil (IUD) works independently of how Mounjaro works in your body. Tirzepatide does not reduce the coil's contraceptive effectiveness. However, if you're also taking oral contraceptive pills alongside the coil, Mounjaro may reduce their absorption—discuss this with your prescriber. Q2: Can I use Mounjaro while I have a coil fitted? A2: Yes, you can use Mounjaro with a coil fitted. The coil will continue to work as normal. Always inform your prescriber about your coil and any other medications or contraceptives you're using so they can assess whether Mounjaro is suitable for you and whether any adjustments are needed. Q3: Does tirzepatide affect hormonal coils like Mirena? A3: No, tirzepatide does not affect how a hormonal coil (like Mirena) releases hormones. The coil releases hormones directly into your uterus, bypassing your digestive system, so Mounjaro's effect on gastric emptying doesn't interfere with it. Q4: What contraception should I use with Mounjaro? A4: Non-oral contraceptives—coils, implants, injections, patches—are not affected by Mounjaro. If you're using oral contraceptive pills, discuss with your prescriber, as Mounjaro may affect absorption. They may recommend a barrier method or switching to a non-oral option. Q5: Should I tell my GP about my coil before starting Mounjaro? A5: Yes, always inform your GP or prescriber about your coil and all other medications and contraceptives. This helps them assess whether Mounjaro is suitable for you and whether any adjustments to your contraception strategy are needed during treatment.- 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.
What is BMI and how is it calculated?
BMI (Body Mass Index) is calculated by dividing your weight in kilograms by your height in metres squared. It's the standard screening tool used by the NHS to assess whether adults are a healthy weight.
Is BMI accurate for everyone?
BMI is a useful screening tool but doesn't account for muscle mass, bone density, or body fat distribution. Athletes may have a high BMI without excess fat. The NHS recommends using BMI alongside waist circumference for a more complete picture.
What are GLP-1 medications like Mounjaro and Wegovy?
GLP-1 receptor agonists are prescription medications that mimic gut hormones to reduce appetite and help with weight loss. Mounjaro (tirzepatide) and Wegovy (semaglutide) are the two most widely used for weight management in the UK.
Am I eligible for GLP-1 weight loss medication in the UK?
Generally, you need a BMI of 30+ (obese) or 27+ with a weight-related health condition. You must be 18 or over. Use our BMI calculator to check.
What is the difference between Mounjaro and Wegovy?
Mounjaro (tirzepatide) is a dual GIP/GLP-1 agonist with up to 22.5% weight loss. Wegovy (semaglutide) is GLP-1-only with up to 15-17% weight loss. Both are weekly injections.
Is this website free to use?
Yes, 100% free. No sign-up required. All tools work instantly in your browser and no personal data is stored on our servers.
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.