Which drugs cut the contraceptive effect?

Since 1960, when the first oral contraceptives were created, they have changed the way that sex is present in women’s lives.

Although there are known side effects, the pills provide other ways to control birth rates than condoms. However, it is necessary to remember that contraceptives are a medication and can interact with other substances.

Drug interaction is a process that causes a substance to interact in some way with another, be it a food, drink, other medication or any chemical present in the environment.

This interaction can increase or reduce the expected effects.

Read more: How to take a pregnancy test (pharmacy and blood test)?

So it is with oral contraceptives, which can interact with several other medications.

Initially, they brought an enormous amount of hormones. In the last few decades, due to the side effects caused by this, the amount and types of hormones have been adjusted so that the minimum necessary dose is present in it.

Each body is different. Do not forget that your doctor is the best person to indicate which treatments can be combined and do not forget to warn you if you use any medicine.

Among the possible substances to interfere with contraceptives are:



Antibiotics are used to kill bacteria and contain infections. It turns out that this can affect the metabolism of contraceptives.

When the pill is ingested, it is digested in the stomach and the hormones go into the bloodstream. Between 40% and 60% of them are transformed into other substances.

These substances are metabolized in the liver. From the liver, they go to the bile and from there to the intestine. In the intestine, the intestinal flora metabolizes these substances, releasing more active hormones that finally reach the bloodstream to take effect.

The problem is that many antibiotics have an effect on this process. These drugs are not very specific as to which bacteria kill and several of them, such as penicillins and tetracyclines, greatly reduce the amount of microorganisms in the intestine.

This means that substances that would normally release hormones with contraceptive capacity can pass directly through the intestine, since fewer bacteria are there to make this transformation.

In addition, rifampicin (and tetracyclines as well) for example, intensifies the metabolism of the liver, which can reduce the amount of hormone available in the intestine.

Not every antibiotic reduces the effect of the contraceptive. Remember to talk to your doctor about this before you start with a new medication.


Antifungals such as griseofulvin can reduce the effects of contraceptives by reducing the amount of hormones available in a woman’s blood. Risks can include bleeding and even unwanted pregnancies.


Herbal medicines are those that are extracted from medicinal plants and using only plant products.

Some herbal medicines have the effect of reducing the effectiveness of contraceptives. It is the case of the wild heart of palm Serenoa repens ), used for the treatment and relief of symptoms of benign tumors in the prostate, which interacts with the estrogen hormones and can reduce its effects.

Another medicinal plant that reduces the effectiveness of the contraceptive is St. John’s wort ( Hypericum perforatum ), which is usually used to relieve symptoms of anxiety, mild depression, tension and muscle pain. The interaction of substances can reduce the effects of hormones, increasing the chances of an unwanted pregnancy.


Corticosteroid hormones are used mainly as anti-inflammatory and immunosuppressive agents . They are usually produced in the adrenal glands, but they can also be created in the laboratory, so they can be used as medicines.

They do not reduce the effect of contraceptives, but another type of interaction takes place. The side effects of corticosteroids are increased by contraceptives.


Antiretroviral drugs like efavirenz , used to control HIV , can reduce hormone levels in a woman’s body and decrease the effect of the birth control pill. Tell your doctor if you use any of these medications.

Levothyroxine sodium

The levothyroxine sodium is a synthetic hormone which is used for hormone replacement when there are diseases related to thyroid function (such as hypothyroidism ).

The substance does not reduce the effects of the contraceptive pill, but the opposite happens. Levothyroxine has its effect reduced by the pill.

Estrogens increase the amount in the blood of a protein needed to transport thyroid hormones throughout the body. When the amount of this protein is too high, thyroid hormones can get stuck in the bloodstream and not get to where they need to go.

In healthy patients, the thyroid raises hormone production to compensate for this, but when the patient needs to take levothyroxine, it means that the organ is not able to make this compensation.

Therefore, if you take contraceptives and have problems with your thyroid, it is important to talk to your doctor to adjust the doses accordingly.

Derivatives of retinoic acid

Retinoic acid is a vitamin . It is often used as an anti- acne and some derivatives of this acid can affect the effects of contraceptives.

Medicines such as isotretinoin can cause severe deformation of the fetus, so it is necessary for the woman to use some contraceptive method during treatment and the pill is one of the most reliable.

However, this substance has the ability to reduce the effects of the contraceptive, so it is recommended that more than one type of protection is used, such as condoms in conjunction with the pill.

Anticonvulsants and barbiturates

Some anticonvulsants and barbiturates, such as phenytoin , phenobarbital and carbamazepine , among others, can reduce the effects of contraceptives, so it is important to use more than one contraceptive method in this case.

As with antibiotics , not all anticonvulsants cause this drug interaction , but it is important to talk to your doctor about it.


Alcohol, when used frequently, can cause an increased chance of the possible side effects of birth control pills, such as thrombosis.

Overused, over time, can also cause liver problems, which can affect the metabolism of contraceptives and other medications. So it is important not to abuse alcoholic beverages.

Contraceptives are an option for birth control, but it is important to be careful with your interactions to avoid side effects or unwanted pregnancies. Share this text with your friends to let them know more about it!