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 Contraceptive Implant?
If you're considering Mounjaro (tirzepatide) and use a contraceptive implant, you may wonder if the injection affects its effectiveness. The good news is that Mounjaro does not directly interfere with the implant itself. However, there is an important medication interaction you should know about. Mounjaro can slow how quickly some medications are absorbed in the stomach, which may theoretically affect other medications — though evidence specifically linking Mounjaro to implant failure is limited. Always inform your GP or prescriber about all contraception methods before starting Mounjaro, as they may recommend additional precautions during dose adjustments.
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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.
How Mounjaro May Affect Medication Absorption
Mounjaro (tirzepatide) slows gastric emptying — the rate at which food and medications move through your stomach. This is how it helps reduce appetite, but it can theoretically affect the absorption of oral medications taken at the same time. The contraceptive implant releases hormones directly into the bloodstream, so it does not pass through the stomach and should not be affected by Mounjaro's slowing effect on digestion.
However, the UK prescribing information for Mounjaro notes that it may reduce the absorption of oral medications. If you take any oral contraceptives alongside Mounjaro, your GP or prescriber may recommend adding a barrier contraception method or switching to a non-oral form (like the implant, which you already use) during the first 4 weeks of Mounjaro treatment and for 4 weeks after each dose increase. This is a precautionary measure because the drug information is based on how Mounjaro affects stomach function, not implant efficacy directly.
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.
What You Should Do Before Starting Mounjaro
Before your first Mounjaro injection, tell your prescriber that you use a contraceptive implant. Your GP or the online prescriber conducting your clinical assessment will document this. There is no evidence that you need to remove or replace your implant because of Mounjaro, and you do not need separate contraception because the implant works independently of stomach function.
If you are also taking oral contraceptives alongside your implant, or planning to become pregnant, discuss this with your prescriber, as pregnancy is a contraindication for Mounjaro. If you do become pregnant while on Mounjaro, stop the injection immediately and contact your GP or sexual health clinic — the implant can remain in place or be removed depending on your preference and clinical advice.
You can use our free BMI calculator to check whether you meet the eligibility criteria for Mounjaro (BMI 30 or above, or BMI 27–29.9 with weight-related health conditions). Calculate your BMI now to see if prescription weight loss medication might be suitable for you — then discuss the results with your GP during your consultation about Mounjaro and your contraception method.
- 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 contraceptive implant less effective?
No. The implant releases hormones directly into your bloodstream, not through the stomach, so Mounjaro's effect on digestion does not reduce implant effectiveness. The implant remains a reliable form of contraception while taking Mounjaro. Always inform your prescriber you use an implant before starting treatment.
Do I need different contraception when starting Mounjaro?
No, your implant alone is sufficient. However, if you also take oral contraceptive pills, your prescriber may recommend a barrier method (condom) for 4 weeks after each dose adjustment, as Mounjaro may slightly reduce oral medication absorption. This is a precaution, not because the implant fails.
What if I want to become pregnant while on Mounjaro?
You should not take Mounjaro if you are pregnant or planning to become pregnant — it is contraindicated in pregnancy. If you plan to conceive, discuss this with your GP before starting Mounjaro. You can remove your implant and stop Mounjaro when ready to try for a baby.
Should I tell my prescriber about my implant when applying for Mounjaro?
Yes, absolutely. Include your contraceptive implant in your medical history during your online clinical assessment or GP consultation. This helps your prescriber assess your overall health and ensure there are no unexpected interactions or contraindications specific to your situation.
Can I use Mounjaro if I have just had my implant fitted?
Yes, you can start Mounjaro while using an implant. There is no waiting period or contraindication between the two. However, if you have recently started oral antibiotics (which can reduce implant effectiveness), discuss this with your prescriber, as they may recommend temporary barrier contraception.
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.