An herbal preparation isolated from the plant St. John's Wort with photodynamic, antineoplastic, and antidepressant properties. Hypericin, one of the active compounds found in hypericum perforatum, is a photosensitizer that, when exposed to a particular wavelength and intensity of light, may induce tumor cell apoptosis. Another compound, hyperforin, induces caspase-dependent apoptosis in certain tumor cell lines. Hypericum perforatum preparations may also stimulate the activity of cytochrome P450 enzymes and P-glycoprotein drug transporters, resulting in increased metabolism and decreased efficacy of various chemotherapeutic agents and other drugs. (NCI04)