Hypericin. Computer graphic of a molecule of hypericin, a drug which may fight viruses such as Human Immunodeficiency Virus (HIV), papilloma virus, cytomegalovirus, influenza, & hepatitis B. The molecule's atoms are colour-coded: carbon (C) is grey, hydrogen (H) is white and oxygen (O) is red. Hypericin's chemical formula is C30H16O8. The drug is found in low concentrations in St. John's Wort, Hypericum sp., a common plant long used in herbal medicine. Side effects of high doses include an abnormal skin sensitivity to sunlight and other strong light.