The active ingredients of St John's wort, a herb commonly used to treat mild depression, are in doubt after US research revealed that one of them is contained in such small quantities in some brands of the drug that it is ineffective.
A health-newswire report notes that the recent research underlines the continuing doubt over which active ingredient is responsible for the potential benefits of the herbal remedy.
Gerlie De Los Reyes and colleagues at the University of Southern California have brought attention to research suggesting that hyperforin, rather than hypericin, may be the active component of the medication, known officially as Hypericum perforatum. Their findings are published in the American Journal of Health-System Pharmacy.
"Hypericins isolated from the extract have been shown to be virtually inactive as psychotropic agents in animal models," said the researchers.
The team looked at eight commercial brands of St John's wort and found wide variations in the amount of hyperforin that they contained.
They found that only two of the products tested contained enough hyperforin to be clinically therapeutic. While recent reports claim hyperforin to be an active anti-depressant, it is not routinely used to standardise St John's wort products because it degrades under ambient conditions.
"It's essential that manufacturers standardise and list the content of hyperforin on St John's wort labels," said Gerlie De Los Reyes.
She added: "Consumers must have this information to make informed decisions about the medications they are taking."