A study on St. John’s wort (hypericum perforatum) one of the five best-selling herbs in the United States has given rise to suspicion for its intake. Many use it for medicinal purposes as an antidote for depression. Presently the herb has been the subject of growing concern about its interaction with birth control pills, the blood thinner warfarin, and cyclosporin, a medication used with those who have received organ transplants. A new study examining its effect on pregnant women and those who are breast-feeding contributes to the evidence that the product should be used with caution. The study will soon be published in the Canadian Journal of Clinical Pharmacology. By scientifically reviewing, its efficacy of use for different conditions, it was discovered that it has low-level harm during pregnancy and strong evidence of side effects during lactation. The researches concluded: 1. Precaution is required when using St. John wort during pregnancy and lactation. 2. Strong scientific evidence showed that St. John’s wort consumption during lactation did not affect maternal milk production nor affect infant weight, but may cause colic, drowsiness or lethargy. 3. It is an effective aid in combating mild to moderate depression and low-level evidence for other conditions.