Hormonal contraceptives and antibiotics: how do they interact?

By (embryologist) and (embryologist).
Last Update: 05/25/2022

Combined oral contraceptives (COCs), also known as birth control pills, are a hormonal method of contraception. The pill works by preventing ovulation from occurring, increasing the density of cervical mucus and altering the endometrium. Thus, through these mechanisms, these pills prevent pregnancy from occurring.

Taking certain antibiotics may affect the effectiveness of these contraceptives. Therefore, if the woman does not wish to become pregnant, it is important that she is well informed by her doctor about the possible interaction between the two drugs.

Provided below is an index with the 7 points we are going to expand on in this article.

Preliminary concepts

Before discussing the effect of taking antibiotics on the efficacy of contraceptives, it is important to be clear about what these drugs are and what their function is.

What is an oral hormonal contraceptive?

Oral hormonal contraceptives are a contraceptive method that usually combines two active ingredients, corresponding to two hormones: an estrogen and a progestin.

For this reason, these contraceptives are also known as combined oral contraceptives. However, there are also oral contraceptives that contain only the progestin.

Combined oral contraceptives alter the hormonal regulation of the menstrual cycle to prevent pregnancy from occurring. Specifically, these contraceptives prevent the release of the egg (ovulation) and alter the cervical mucus, making it difficult for sperm to ascend. In addition, the uterine lining is also modified, making the implantation of an embryo more complicated.

It is important to mention that it is a contraceptive method that requires a medical prescription for its acquisition. In fact, the specialist must first make sure that the woman does not have any contraindication to take it.

In addition, a woman should always keep in mind that the contraceptive pill does not protect against sexually transmitted diseases(STDs), for which she should use another method of contraception such as a condom.

If you want to read more information about this contraceptive method and how to take it correctly, you can access the following link: What is the contraceptive pill? - Efficacy, how to take it and risks.

What is an antibiotic?

An antibiotic is a medicine indicated to treat infections caused by bacteria. The main function of these drugs is to kill bacteria or hinder their multiplication.

Antibiotics only work against a bacterial infection and not against an infection caused by a virus.

In addition, because bacteria may develop resistance to them, antibiotics should only be taken when prescribed by a specialist.

is there an interaction between contraceptives and antibiotics?

When the contraceptive pill is combined with antibiotics, a woman may be concerned about whether there is an interaction between the two that affects their efficacy (thus leading to an increased likelihood of pregnancy).

The truth is that for most antibiotics there is insufficient scientific evidence to show that they reduce the effect of hormonal contraceptives. However, there is one exception: rifamycins such as rifampicin or rifabutin.

Therefore, in principle, there would be no reason to use a barrier method of contraception (such as a condom) when taking antibiotics, as long as the antibiotic is not a rifamycin (rifampicin or rifabutin).

However, despite the fact that antibiotics generally do not influence the contraceptive effect, some specialists opt for prevention. Therefore, they recommend additional precautions in cases where any antibiotic is combined with a hormonal contraceptive (and even up to 7 days after the end of antibiotic treatment).

Rifampicin and contraceptives

Rifampicin is an antibiotic used for the treatment of tuberculosis, among other possible indications. This antibiotic induces the liver enzymes required for the metabolism of combined hormonal contraceptives.

Thus, this situation causes a decrease in the hormonal levels of the contraceptive, which would lead to a reduction in its effectiveness. Thus, the joint use of rifampicin with combined oral contraceptives (but also, for example, contraceptive patches or rings) would increase the possibility of unwanted pregnancy.

On the other hand, rifabutin seems to have less effect on the metabolism of combined contraceptives than rifampicin. However, rifabutin may also reduce contraceptive effectiveness.

Therefore, if the combined contraceptive user is going to take rifampicin or rifabutin, it is recommended that she take additional or alternative contraceptive measures to avoid pregnancy. Therefore, the woman should agree with the specialist on the measures to be taken, as well as the time she should carry them out.

However, the use of progesterone-only injectable contraceptives, as well as the use of intrauterine devices (IUDs) in non-pelvic tuberculosis, does appear safe with rifamycins.

Drugs interacting with contraceptives

In addition to the antibiotics rifampicin and rifabutin, there are other drugs that could influence the efficacy of combined oral contraceptives. Among them are some drugs to treat:

  • Epilepsy: barbiturates, carbamazepine, phenytoin, primidone, felbamate, oxcarbazepine, topiramate...
  • Hepatitis C or HIV infection: ritonavir, nevirapine, efavirenz, etc.
  • Fungal infections: griseofulvin.

In addition, preparations containing St. John's wort may also reduce the effectiveness of the contraceptive pill. Therefore, when a woman is taking hormonal contraceptives, it is important to tell her doctor before taking a medication or herb.

FAQs from users

Are there any symptoms that indicate that the antibiotic is reducing the effectiveness of the contraceptive?

By Andrea Rodrigo B.Sc., M.Sc. (embryologist).

Intermenstrual bleeding (metrorrhagia), i.e. between one menstrual period and the next, may be caused by hormonal imbalance. This is unusual during hormonal treatment with contraceptives since, if taken properly, regulation is strict. Therefore, having a breakthrough bleeding may indicate a failure of regulation, perhaps caused by the interaction with the antibiotic.

Does this interaction occur only with oral contraceptives or also with other types of hormonal contraceptives?

By Andrea Rodrigo B.Sc., M.Sc. (embryologist).

Although most studies refer to oral contraceptives, the indications regarding the effect of antibiotics generally apply to other types of hormonal contraceptives such as injections, subdermal implants, the vaginal ring and patches.

Besides antibiotics, are there any other medications that can affect the hormonal regulation of birth control pills?

By Andrea Rodrigo B.Sc., M.Sc. (embryologist).

Whenever a woman is going to take a medication during treatment with contraceptives, it is advisable to consult with the specialist about the possible interaction between the two. This advice is given not only because of the possibility of pregnancy due to the loss of contraceptive effectiveness, but also because the contraceptive could reduce the effect of the indicated medication.

In addition to rifampicin, other types of drugs that show interaction with oral contraceptives are anticonvulsants such as phenytoin, phenobarbital, primidone, bitobarbital, carbamazepine, ethosuximide or methylphenolbarbital.

For other specific medications, as we have already mentioned, it is advisable to consult with the physician, since the studies are not very clear and, in addition, there may be specific changes due to the situation of each woman.

Can I take birth control pills and an antibiotic for urinary tract infection?

By Silvia Azaña Gutiérrez B.Sc., M.Sc. (embryologist).

Yes, the most commonly used antibiotics have not been shown to have a reducing effect on the efficacy of contraceptive pills.

In general, a decrease in the contraceptive effect of taking oral contraceptives and antibiotics together has only been demonstrated with rifampicin and rifabutin.

In any case, it is recommended that you consult a specialist before taking any type of medication or herb, in case an additional or alternative contraceptive method to contraceptive pills is necessary.

If you want to read more information about the contraceptive injection, you can visit the following link: What is the contraceptive injection and how is it used?

On the other hand, if you are interested in the IUD, we recommend you read this article: How Does the IUD Work and What are the Pros & Cons?

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FAQs from users: 'Are there any symptoms that indicate that the antibiotic is reducing the effectiveness of the contraceptive?', 'Does this interaction occur only with oral contraceptives or also with other types of hormonal contraceptives?', 'Besides antibiotics, are there any other medications that can affect the hormonal regulation of birth control pills?' and 'Can I take birth control pills and an antibiotic for urinary tract infection?'.

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Authors and contributors

 Andrea Rodrigo
Andrea Rodrigo
B.Sc., M.Sc.
Bachelor's Degree in Biotechnology from the Polytechnic University of Valencia. Master's Degree in Biotechnology of Human Assisted Reproduction from the University of Valencia along with the Valencian Infertility Institute (IVI). Postgraduate course in Medical Genetics. More information about Andrea Rodrigo
 Silvia Azaña Gutiérrez
Silvia Azaña Gutiérrez
B.Sc., M.Sc.
Graduate in Health Biology from the University of Alcalá and specialized in Clinical Genetics from the same university. Master in Assisted Reproduction by the University of Valencia in collaboration with IVI clinics. More information about Silvia Azaña Gutiérrez
License: 3435-CV

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