Oral Contraceptive ‘Pill’ Failure – Other Drugs, Antibiotics

The oral contraceptive, often referred to as ‘the pill’, is still among the most popular method of preventing an unplanned or unwanted pregnancy. While other forms of contraception, like the contraceptive injection, are widely used, especially after having a child and in developing countries due to the cost, an oral contraceptive is the method of choice for many teens and young women.

How does the oral contraceptive pill work?

The oral contraceptive delivers high doses of estrogen and progesterone to the body, thereby mimicking pregnancy. The body is ‘fooled’ to believe that ovulation should not occur due to the state of perceived pregnancy and through this mechanism, the pill prevents pregnancy. Unlike other forms of the contraception, the oral contraceptive pill requires discipline and fastidiousness on the part of the user and missing the pill, even for one day, can hamper its function.

Oral Contraceptives and Antibiotics

While the oral contraceptive is a very effective form of contraception if taken according to directions, certain drugs and medical conditions can affect its action. The most common drug known for interacting with an oral contraceptive and causing failure of the pill, is an antibiotic. Antibiotic therapy may disturb the natural intestinal flora (bacteria in the bowels) and this hampers the absorption of the pill. A reduced absorption alters the hormone levels needed to ‘trick’ the body into believing that a state of pregnancy already exists. This leads to failure of the oral contraceptive and possibly resulting in unplanned pregnancy.

Antibiotics are one of the most commonly prescribed drugs, second to analgesics (pain killers), and in most cases, it does not interefere with the absorption of the pill. However, it is important to be cautious when using an antibiotic and other forms of contraception, like the condom should be considered if possible failure of the oral contraceptive is suspected. Your doctor should be informed of your oral contraceptive use when you visit him or her for any condition that may require the use of antibiotics.

Drug Interaction and Herbal Remedies with the Oral Contraceptive Pill

Other drugs and chemical compounds that are known to affect the efficacy of the oral contraceptive are antiepileptic drugs. If you suffer with epilepsy, antiepileptic drugs are necessary for the management of your condition and in these cases you should not rely entirely on the pill as a form of contraception. Speak to your doctor about other methods of contraception that could be considered in your case. Herbal remedies like St. John’s Wort (Hypericum perforatum) has also been reported to compromise the oral contraceptive pill and while this remedy can be purchased over the counter, it is important to first consult with your doctor or pharmacist. New research has revealed that other herbal remedies may also lead to the failure of oral contraceptives.

Diarrhea, Vomiting (Gastric Flu) and the Oral Contraceptive Pill

Lastly, diarrhea and vomiting, common symptoms during the gastric flu or in cases of traveler’s diarrhea, may also affect the absorption of the oral contraceptive. If you have suffered with a bout of diarrhea and vomiting, your oral contraceptive may not offer the same level of protection. As a precaution, do not partake in unprotected sex within the first seven days after your bout of diarrhea and vomiting ceases.


  1. Contraception. Netdoctor.co.uk
  2. Oral Contraceptives. Mayo Clinic

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