Pharmacology of St. John’s Wort

Pharmacological properties of St. John’s wort include antidepressant, antiviral, and antibacterial that are related to its primary bioactive constituents

St. John’s wort is traditionally utilized because of its antidepressant pharmacological properties.  St. John’s wort also has antiviral and antibacterial properties.  These diverse pharmacological properties are related to the diverse constituents of the plant.  

The primary constituents of St. John's wort include the napthodianthrones (hypericin and pseudohypericin), acylphloroglucinols (hyperforin and adhyperforin), flavonol glycosides, biflavones, proanthocyanidins, and phenylpropanes (chlorogenic acid and caffeic acid).  

Aphios ResearchersResearch at Aphios has demonstrated that hyperforin is one of the major constituents of St. John’s wort responsible for its serotonin re-uptake inhibition activity and antidepressant properties (Castor, 2001). 

Research at Aphios has also demonstrated that hypericin has no impact on serotonin re-uptake inhibition (Castor, 2001) but has significant impact on antiviral properties (Ilyinskii et al., 2006).  Hypericin is also primarily responsible for the antibacterial properties of St. John’s wort and its photosensitivity.  In fact, the photosensitive nature of hypericin is responsible for its antiviral and antibacterial properties.

Xantol DS™ is standardized hyperforin content and its serotonin re-uptake inhibition activity against.  Xantol DS does not contain hypericin.

Antidepressant Properties

The use of Hypericum extracts for the treatment of mild to moderate depression is the most extensive of all the medical uses of St. John’s wort.  Hyperforin is the major constituent responsible for antidepressant activity, and it has been shown to inhibit the uptake of 5-HT3 serotonin, dopamine, and noradrenaline.  Hyperforin also has affinity for GABA and glutamate transporters. Learn more

Antiviral Properties

Hypericum constituent hypericin has antiviral activity against cytomegalovirus, herpes simplex, human immunodeficiency virus type 1, influenza virus A, Moloney murine leukemia virus, and sindbis virus. Learn more

Antibacterial Properties

Hypericin in St. John’s wort also appears to have broad-spectrum antimicrobial activity. The organisms studied include Staphylococcus aureus (Staph), Streptococcus mutans (Strep) and Escherichia coli (E. coli). Learn more


The photosensitive properties of St. John’s wort are primarily related to its Hypericin content. Learn more


  • Castor TP. (2001).  Methods for Making Hypericum Fractions and St. John’s Wort Products. U.S. Patent 6,291,241.
  • Ilyinskii P, Lallos L and Castor TP. (2006). Inactivation of Viral Infections by Chemiluminescence Activated Light-Sensitive Compounds. U.S. Patent No. 7,037, 5334.