Hypericin is a naphthodianthrone, an anthraquinone derivative which, together with hyperforin, is one of the principal active constituents of Hypericum (Saint John's wort).

The current belief is that the mechanism of antidepressant activity is due to the inhibition of re-uptake of certain neurotransmitters.

[2] The large chromophore system in the molecule means that it can cause photosensitivity when ingested beyond threshold amounts.

[citation needed] In addition, hypericin is under research as an agent in photodynamic therapy, whereby a biochemical is absorbed by an organism to be later activated with spectrum-specific light from specialized lamps or laser sources, for therapeutic purposes.

[citation needed] The antibacterial and antiviral effects of hypericin are also believed to arise from its ability for photo-oxidation of cells and viral particles.