St. John's wort (Hypericum perforatum) is a five-petal yellow flower that has been used medicinally since antiquity.
One of the earliest references to the name St. John's wort is noted in a Gaelic legend from the 6th century where the missionary St. Columba carried a piece of St. John's wort because of his high regard for St. John. It is believed that the name may have been derived from the fact that the flowers bloom around June 24th, the birthday of St. John the Baptist. Wort represents the old English term for plant.
St. John’s wort is widely used as an antidepressant. Clinical trials show it is effective in mild to moderate depression, said to be equivalent to TCAs but with fewer side effects. It is generally well tolerated; commonly reported adverse effects include gastrointestinal symptoms (nausea, abdominal pain, loss of appetite, diarrhea), dizziness, confusion, fatigue, sedation, dry mouth, restlessness, and headache.
The clinical concerns regarding St. John’s wort are related to herb-drug interactions caused by induction of the CYP3A4 and P-glycoprotein systems. This can lead to increased metabolism and loss of efficacy of a range of drugs including anticoagulants, antiretrovirals, antifungals, immunosuppressive agents, opioids, digoxin, and hormonal contraceptives.
In addition, St. John’s wort acts as a serotonin re-uptake inhibitor and may cause or contribute to the serotonin syndrome.

Adapted from Wikipedia, the free encyclopedia. Internet. Accessed on July 14, 2017.