Chemical Constituents of St. John's Wort

Without much difficulty, scientists have been able to determine many of the chemical constituents contained within St. John’s Wort. There are, however, many other compounds that have not yet been discovered which will ultimately shed even more light on the use and application of St. John’s Wort. To date, current research has identified at least ten groups of components thought to contribute to the pharmacological effects of St. John’s Wort. (39) Of these, two primary classes are thought to be the most active: naphthodianthrones and flavanoids. (40) These have been touted as being the primary players in the therapeutic and medicinal action of St. John’s Wort; however, there are many more compounds which act in a complementary role, bringing synergy to the plant as a whole. Depending on what part of the plant is used and when it is harvested or picked, chemical constituents can be found in greater concentrations, boosting their specific therapeutic benefits. (41)

The first class - naphthodianthrones - is the umbrella for a class of chemical constituents called quinones, which contain two of the most studied chemicals thought to be responsible for the anti-depressive action of St. John’s Wort: hypericin and pseudohypericin. When used for
scientific testing, these compounds are chemically extracted and isolated out of the whole plant, and prepared in a laboratory under strict scientific guidelines in order to obtain a new, standardized extract, typically set at 0.3 percent hypericin or 30 percent. (42)

This extraction is said to be necessary in order to accurately measure dosages for purposes of scientifically testing the medicinal effects of St. John’s Wort. Herbalists and many natural practitioners contend that by using just one isolated compound such as hypericin, test results will not be accurate as the complimentary action of all the chemical constituents would not have been taken into account.

These quinones are a type of alkaloid that contain naturally occurring compounds which are easy to spot in plants that display red, yellow or orange pigments. (43) Therefore, the quinines hypericin and pseudohyperidin are found in the greatest concentration in the flower petals and buds of St. John’s Wort. (44) Historical documents record that when cattle and other pasture fed animals have been exposed to large amounts of St. John’s Wort and allowed to eat freely, they experienced heightened sun sensitivity. In rare cases, this has resulted in severe sunburn or even death. (45)

It has been reported that both of these chemicals, when tested on human subjects using a standardized extract, do contain photosensitive properties. (46) However, if a whole plant preparation is used in moderation, there is no indication of any side effects. Based on experimental studies, it would take approximately 30-50 times the recommended daily dose of 900 mg, using the standardized extract, to produce severe phototoxic effects in humans. (47)

The second class of active compounds are known as flavanoids, a large group of biologically active molecules that fall under the umbrella of polyphenols. (48) The flavanoids
present in St. John’s Wort include proanthocyanidin, hyperin, biflavone, amentoflavone and quercetin among others. (49) Flavanoids are found in the highest concentrations in the hypericum flowers.

Other chemical compounds that have been identified include terpenoids, which contain essential or volatile oils, xanthones and coumarins. Many of these compounds, found primarily in the leaves and flowers, are minor chemical components providing balance and completeness that otherwise would be lacking. (50)

Another compound found in St. John’s Wort are tannins, a subgroup of the large phenol class. These tannins are responsible for much of the medicinal action relating to superficial wound or injury care. The greatest concentrations of these chemicals are also found in the leaves and flowers. (51)

Much extensive research has been completed in an attempt to list all the known chemicals found in St. John’s Wort. Scientists have worked diligently, compiling a comprehensive list of these compounds and their estimated percentages. (52)