WASHINGTON  —  The Food and Drug Administration (search) is warning that a study has suggested that the antidepressant Paxil may be associated with birth defects.

Paxil's manufacturer, GlaxoSmithKline (search), said it will include the results of the study in the drug's list of precautions.

A retrospective study found increased numbers of babies born with birth defects to women who were taking Paxil (search) during the first trimester of pregnancy, as compared with women on other antidepressants, according to the FDA and the company.

This included an increase in heart defects, according to a letter from GlaxoSmithKline to health care professionals. The FDA released the letter Tuesday.

The drug, which goes by the generic name paroxetine, is already classified as a "Category C" drug for pregnant women — meaning comprehensive studies of its effects on a pregnancy have not been performed.

Doctors are advised "to carefully weigh the potential risks and benefits of using paroxetine therapy in women during pregnancy. It is recommended that health care providers discuss these latest findings ... as well as treatment alternatives, with their patients," GlaxoSmithKline said.

Based on the study, the company said it has not concluded there exists a definite, causal link between the drug and the increased incidence of birth defects. GlaxoSmithKline cited another survey of births that it said does not note a comparable increase.