Impact of Antibiotics on Birth Control: What You Need to Know

Drug interactions

I would like to ask about having had a urinary tract infection and taking cephalexin.
However, the day after finishing the course of antibiotics, I had intercourse with my boyfriend, and he ejaculated inside me.
I have been consistently taking my birth control pills on time, and I spaced out the intake of the antibiotic and the birth control.
I want to know if there will be any impact.
If so, do I need to take emergency contraception?

Ta, 20~29 year old female. Ask Date: 2022/12/27

Dr. Zhang Kunmin reply Obstetrics and Gynecology

Hello, the following medications may interact with oral contraceptives:
1.
Antibiotics (Penicillin, Cephalosporins, Erythromycin, Sulfonamides, Bactrim, Chloramphenicol, Doxycycline) can reduce the effectiveness of oral contraceptives.
When taking these medications, alternative contraceptive methods should be used, as they may decrease the gut flora that aids in absorption, thereby lowering the effectiveness of the contraceptive.
2.
Sedatives (Barbiturates) can increase the metabolism of oral contraceptives, reducing their effectiveness.
3.
Antiepileptic drugs (Primidone, Phenytoin, Carbamazepine) can also increase the metabolism of oral contraceptives, leading to decreased effectiveness.
4.
Antituberculosis medications (Rifampicin, Isoniazid).
5.
Antidiabetic medications (Rosiglitazone).
6.
Acetaminophen and Ascorbic acid (Vitamin C) may inhibit the metabolism of estrogen, potentially increasing its concentration in the body and leading to a higher incidence of side effects.
7.
Oral contraceptives can affect the action of anticoagulants.
8.
Smoking can increase the metabolism of oral contraceptives, reducing their effectiveness.
9.
Long-term consumption of tea or certain herbs may have additive or subtractive effects with oral contraceptives.
Additionally, any medication should be taken with water and not with tea, coffee, or other beverages, as this may affect the medication's efficacy.
Therefore, if you need to take any of the aforementioned medications while on oral contraceptives, it is advisable to use additional contraceptive measures for seven days, and consider emergency contraception if necessary.
Thank you! Wishing you peace and health, Dr.
Zhang.

Reply Date: 2022/12/27

More Info

When it comes to the interaction between antibiotics and birth control pills, it's important to understand how certain antibiotics can potentially affect the efficacy of hormonal contraceptives. In your case, you mentioned taking cephalexin, which is a type of cephalosporin antibiotic. Generally, most antibiotics do not significantly interfere with the effectiveness of birth control pills. However, there are some exceptions, most notably with rifampin and rifabutin, which are used to treat tuberculosis and some other infections. These antibiotics can reduce the effectiveness of hormonal contraceptives.

In your situation, since you took cephalexin and have been consistently taking your birth control pills as prescribed, the risk of unintended pregnancy is quite low. The timing of your antibiotic use and the fact that you took your birth control pills correctly further reduce this risk. The key factor is that you maintained a proper schedule with your contraceptive method, which is crucial for its effectiveness.

Regarding your concern about having unprotected intercourse the day after completing your antibiotic course, it is unlikely that cephalexin would have any lasting impact on the effectiveness of your birth control pills. The hormonal levels in your body from the contraceptive should remain stable, assuming you have been taking them consistently.

As for the question of whether you should take emergency contraception (the "morning-after pill"), it is generally not necessary if you have been taking your birth control pills correctly and consistently. However, if you have any doubts or if you missed any doses of your birth control pills during the cycle, it might be prudent to consult with a healthcare provider. They can provide personalized advice based on your specific circumstances and medical history.

In summary, while some antibiotics can affect the efficacy of birth control pills, cephalexin is not one of them. If you have been diligent in taking your birth control as directed, the likelihood of pregnancy is very low. If you have any lingering concerns or experience any unusual symptoms, it is always best to reach out to a healthcare professional for further guidance. They can help clarify any uncertainties and provide reassurance regarding your contraceptive method and overall reproductive health.

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