“While this herb does have legitimate antidepressant properties, I generally advise against its use due to concerns that outweigh its potential benefits.”What is St. John’s wort? St. John’s wort, or Hypericum perforatum, is a plant with bright yellow, star-shaped flowers that blooms around June 24th—St. If you already take prescription antidepressants, taking St. John’s wort can lead to a potentially life-threatening increase in serotonin, psychiatrists warn. St. John’s wort also increases levels of liver enzymes like CYP3A4, which speed up the breakdown of many medicines in the liver. Goel points out that it may take several weeks before the benefits of St. John’s wort are noticeable.