Herb-Drug Interactions: St John’s wort

Hypericum perforatum L. (Clusiaceae) Synonym(s) and related species Hypericum, Millepertuis. Hypericum noeanum Boiss., Hypericum veronense Schrank. Pharmacopoeias St John’s Wort (British Ph 2009, European Ph 2008, US Ph 32); St John’s Wort Dry Extract, Quantified (British Ph 2009, European Ph, 6th ed., 2008 and Supplements 6.1, 6.2, 6.3 and 6.4). Constituents The main groups of active constituents of St John’s wort are thought to be the anthraquinones, including hypericin, isohypericin, pseudohypericin, protohypericin, protopseudohypericin and cyclopseudohypericin, and the prenylated phloroglucinols, including hyperforin and adhyperforin. Flavonoids, which include kaempferol, quercetin, luteolin, hyperoside, isoquercitrin, quercitrin and rutin; biflavonoids, which include biapigenin and amentoflavone, and catechins are also present. Other polyphenolic constituents include caffeic and chlorogenic acids, and a volatile oil containing methyl-2-octane. Most St John’s wort products are standardised at least for their hypericin content (British Pharmacopoeia 2009), even though hyperforin is known to be a more relevant therapeutic constituent, and some preparations are now standardised for both (The United Read more […]

Herb-Drug Interactions: Milk thistle

Silybum mahanum (L.) Gaertn. (Asteraceae) Synonym(s) and related species Lady’s thistle, Marian thistle, Mediterranean milk thistle, St Mary’s thistle. Carduus marianus, Mariana lactea Hill. Pharmacopoeias Milk Thistle (US Ph 32); Milk Thistle Capsules (US Ph 32); Milk Thistle Fruit (British Ph 2009, European Ph 2008); Milk Thistle Tablets (US Ph 32); Powdered Milk Thistle (US Ph 32); Powdered Milk Thistle Extract (US Ph 32); Refined and Standardised Milk Thistle Dry Extract (British Ph 2009, European Ph, 6th ed., 2008 and Supplements 6.1, 6.2, 6.3 and 6.4). Constituents The mature fruit (seed) of milk thistle contains silymarin, which is a mixture of the flavonolignans silibinin (silybin), silicristin (silychristin), silidianin (silydianin), isosilibinin and others. It may be standardised to contain not less than 1.5% (European Ph, 6th ed., 2008 and Supplements 6.1, 6.2, 6.3 and 6.4), or not less than 2% (The United States Ph 32) of silymarin, expressed as silibinin (dried drug). Standardised extracts, containing high levels of silymarin, are often used. Milk thistle fruit also contains various other flavonoids, such as quercetin, and various sterols. Note that milk thistle leaves do not contain silymarin, Read more […]