Will Emergency Contraceptive Pills Work After Antibiotic Use?

Taking antibiotics

Doctor, I would like to ask, I had my period just ended and had sexual intercourse with my boyfriend twice.
I took cold medicine and antibiotics at 10 AM, then took the emergency contraceptive pill around 2 or 3 PM, and took the cold medicine again at 7:30 PM.
Will the emergency contraceptive pill be ineffective?

Tina, 20~29 year old female. Ask Date: 2016/05/30

Dr. Zhang Kunmin reply Obstetrics and Gynecology

Hello, the effectiveness of emergency contraceptive pills taken within 72 hours after intercourse is about 97%.
However, it is not 100%, and there is a failure rate of approximately 3%.
Antibiotics may potentially affect their effectiveness.
It is recommended to check for pregnancy if your period is more than a week late.
Thank you! Wishing you safety and health.
Dr.
Zhang

Reply Date: 2016/05/30

More Info

Emergency contraceptive pills (ECPs) are designed to prevent pregnancy after unprotected intercourse or contraceptive failure. The effectiveness of ECPs can be influenced by various factors, including the timing of administration, the type of ECP used, and potential interactions with other medications, including antibiotics.

In general, most antibiotics do not significantly affect the efficacy of emergency contraceptive pills. The primary concern arises with specific antibiotics, such as rifampin and rifabutin, which are known to induce liver enzymes that can decrease the effectiveness of hormonal contraceptives, including ECPs. However, the majority of commonly prescribed antibiotics, such as those used for respiratory infections or urinary tract infections, do not have this effect.

In your case, you mentioned taking a cold medication that includes antibiotics in the morning and then taking an emergency contraceptive pill later in the day. If the antibiotic you took is not one of the enzyme-inducing types (like rifampin), then it is unlikely to interfere with the effectiveness of the emergency contraceptive pill.
It is also important to consider the timing of when you took the ECP. ECPs are most effective when taken as soon as possible after unprotected intercourse, ideally within 72 hours, and their effectiveness diminishes the longer you wait. Since you took the ECP a few hours after the sexual encounter, you are still within the effective window.

Regarding your concern about taking the cold medication again later in the evening, as long as the antibiotic is not one that significantly interacts with hormonal contraceptives, it should not affect the ECP's effectiveness. However, it is always a good practice to consult with a healthcare provider or pharmacist about any medications you are taking, especially when it comes to potential interactions.

In summary, if the antibiotic you took is not one of the known enzyme inducers, the emergency contraceptive pill you took should still be effective. If you have any lingering concerns or if you experience any unusual symptoms, it is advisable to follow up with your healthcare provider for personalized advice and guidance. They can provide you with the most accurate information based on your specific situation and the medications involved.

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