Medications
Mounjaro and Contraception: What Women in New Zealand Need to Know
Important guidance on oral contraceptive effectiveness while taking Mounjaro. Learn what to do.
Well Revolution
February 11, 2026
If you're taking or considering Mounjaro (tirzepatide) for weight loss and use oral contraceptives, there's important information you need to be aware of. Regulatory agencies worldwide (including Australia's TGA, the UK's MHRA, and the US FDA) have updated their guidance on how Mounjaro may affect the effectiveness of the contraceptive pill.
This isn't cause for alarm, but it does require attention and, in many cases, a conversation with your prescriber about your contraception choices.
The Key Issue: Oral Contraceptives May Be Less Effective
Mounjaro works in part by slowing gastric emptying, which is how quickly food and medications move through your stomach. This is one of the reasons it helps with weight loss (you feel fuller for longer) and blood sugar control. However, this same mechanism can affect how well oral medications are absorbed, including the contraceptive pill.
In December 2025, Australia's Therapeutic Goods Administration (TGA) updated the product information for tirzepatide after investigating this potential interaction. Their conclusion: reduced effectiveness of oral contraceptives "could not be ruled out." As a precautionary measure, they now advise additional contraceptive protection.
What the Science Shows
Clinical pharmacology studies have measured exactly how tirzepatide affects oral contraceptive absorption. When researchers gave women a single 5mg dose of tirzepatide along with a combined oral contraceptive containing ethinyl estradiol and norgestimate, they found:
- Peak blood levels of ethinyl estradiol dropped by 59%
- Peak levels of the progestogen components dropped by 55–66%
- Overall exposure (total amount absorbed) was reduced by 20–23%
- The time to reach peak concentration was delayed by about 2.5 hours
This effect is most pronounced after the first dose and after each dose increase. The good news is that it diminishes over time as your body adjusts to the medication.
The Official Guidance
Based on this evidence, regulatory agencies and clinical guidelines now recommend that if you're using oral hormonal contraceptives while taking Mounjaro, you should:
Option 1: Add a barrier method
Use condoms or another barrier method for four weeks after starting Mounjaro and after each dose increase.
Option 2: Switch to a non-oral contraceptive
Consider changing to a contraceptive method that isn't affected by gastric emptying, including:
- Hormonal IUD (Mirena)
- Copper IUD
- Contraceptive implant (Jadelle)
- Contraceptive injection (Depo-Provera)
- Vaginal ring
- Contraceptive patch
Why This Matters More Than You Might Think
1. Weight loss can improve fertility
Significant weight loss can restore ovulation in women who weren't ovulating regularly before. Research shows that even modest weight loss (5–10% of body weight) can help women with irregular cycles or PCOS start ovulating again. This has led to what social media calls "Ozempic babies" - unexpected pregnancies in women who thought they had fertility issues.
2. Mounjaro is not recommended during pregnancy
Animal studies have shown potential risks to foetal development, and there isn't enough human data to confirm safety. The combination of potentially reduced pill effectiveness, improved fertility from weight loss, and the recommendation to avoid the medication during pregnancy makes reliable contraception particularly important.
What About Side Effects and the Pill?
Beyond the absorption issue, common gastrointestinal side effects of Mounjaro can also affect how well the pill works:
- Vomiting: If you vomit within 2–3 hours of taking your pill, it may not have been fully absorbed. Follow the missed pill rules.
- Severe diarrhoea: Prolonged diarrhoea (more than 24 hours) can reduce absorption. Use backup contraception during and for 7 days after.
Is This Issue Unique to Mounjaro?
Among GLP-1 and GIP receptor agonist medications, the contraceptive interaction appears most significant with tirzepatide. Studies on other medications have generally not found a clinically significant effect:
- Semaglutide (Ozempic, Wegovy): No significant effect demonstrated
- Liraglutide (Saxenda): No significant effect demonstrated
- Dulaglutide (Trulicity): No significant effect demonstrated
However, all GLP-1 medications can cause vomiting and diarrhoea that might reduce pill absorption.
Planning for Pregnancy
If you're considering pregnancy:
- Stop Mounjaro at least two months before trying to conceive to allow the medication to clear from your system
- Talk to your prescriber about alternative approaches to weight management during pregnancy
- Don't panic if you become pregnant on Mounjaro: Stop the medication and contact your healthcare provider promptly, but a recent BMJ study found no increased risk of major birth defects from first-trimester exposure
The Bottom Line
The interaction between Mounjaro and oral contraceptives is manageable with the right approach:
- Use barrier contraception or switch to a non-oral method for four weeks after starting Mounjaro and after each dose increase
- Weight loss can improve fertility, so reliable contraception matters even more
- Stop Mounjaro at least two months before trying to conceive
Talk to your healthcare provider about what approach makes the most sense for your situation.
References
- Therapeutic Goods Administration (TGA). Updated contraception advice for Mounjaro (tirzepatide). December 2025.
- Faculty of Sexual and Reproductive Healthcare (FSRH). GLP-1 agonists and oral contraception statement. February 2025.
- Medsafe New Zealand. Mounjaro (tirzepatide) Data Sheet. December 2025.
- U.S. FDA. MOUNJARO Prescribing Information. 2025.
- Skelley JW, et al. Journal of the American Pharmacists Association. 2024.
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