Study: Antibiotics ‘may reduce effectiveness of contraceptives’

Taking antibiotics may reduce the effectiveness of birth-control pills, researchers have said.

In a study, published in the British Medical Journal’s Evidence Based Medicine, scientists advise women should take extra precautions to avoid unwanted pregnancy when they are on antibiotics.

They wrote: “This evidence suggests there is an interaction of antibacterial drugs with hormonal contraceptives, which can potentially impair the effectiveness of the contraceptives.

“The precautionary principle dictates that women taking hormonal contraceptives should be advised to take extra contraceptive precautions when a short course of an antibacterial drugs is added.”

But experts say most contraceptive pills in the UK come with warnings about possible reduced effectiveness when also taking some other drugs, including antibiotics.

Stephen Evans, a professor of pharmacoepidemiology at the London School of Hygiene & Tropical Medicine, who was not involved in the study, said: “It seems likely that the patient leaflets are not read, and it is possible that some prescribers do not mention the problem, or that patients forget they were told.”

The scientists, led by Jeffrey K Aronson, of the Nuffield Department of Primary Care Health Sciences at Oxford University, looked at the data gathered through the Yellow Card Scheme run by the Medicines and Healthcare products Regulatory Agency (MHRA), the UK’s drug and medical devices regulator.

Among other things, the scheme collects information on unwanted side-effects of different types of drugs.