Introduction: World wild use of complementary medicine especially herbal remedies and inadequacy of evidences for safety and efficacy of medicinal herbs during pregnancy is an important subject and needs especial attention. This study was performed to assess the knowledge of pregnant women in Tehran about the efficacy and safety of herbal medicine and their practice during pregnancy.

  Methods: In this cross-sectional study which was conducted in Tehran in 1390, 600 pregnant women were in gestational age more than 32 weeks or 1 week after childbirth were collected from governmental hospitals by multistage sampling method and were studied. Data gathering tool was a researcher made questionnaire including questions about demographic characteristics, some information about pregnancy, the use of herbs in pregnancy, awareness of the effects and safety of herbs and their source of information. Data analyzed by student T tests and chi-square test.

  Results: Four hundred and two patients (67%) of the sample had used at least one type of herbal medicine during their current or previous pregnancies with a mean of 2.71 ± 1.94 herbs per individual. Two commonly used herbs were peppermint (32.8%) and olibanum (26.3%). The women’s information about the indications for using herbal medicine was mainly funded from sources other than physicians. In many cases, non-established indications for the use of herbs were mentioned. Also, more efficacy and safety of herbal remedies were mentioned as the main cause for using them.

  Conclusion: The knowledge about medicinal plants and their safety and efficacy in pregnant women is not enough. Considering the high frequency of herbal medicine use during pregnancy, pregnant women need appropriate sources of information about these medicines. Further, health care providers should ask pregnant women about taking herbal medicines.