Advice issued by The National Institute for Public Health and the Environment (RIVM) identifies the reduced effect of chemotherapy or agents against fungal or viral infections as one possible side effect.
Other outcomes observed when consuming herbal preparations or remedies containing St. John's wort include an enhanced effect of antidepressants or sedatives.
“There are indications for genotoxicity and reproductive and developmental toxicity,” RIVM’s report warns of food supplements containing St John’s wort. “Chronic toxicity/carcinogenicity data are lacking.
“Owing to omissions in the toxicological profile of St John’s wort extract and its constituents, no firm conclusions can be drawn on these aspects.”
“Details on the composition of these food supplements are often lacking and the composition can vary greatly. Therefore, the precise effects are difficult to determine.
Hypericin et al
St John’s wort (Hypericum perforatum L.) is used in food supplements and herbal teas preparations that are said to enhance mood and sleep amongst other benefits.
Relevant constituents for the pharmacological effects of St John’s wort includes hypericin, pseudohypericin and hyperforin.
In the Netherlands, there are no specific restrictions for the use of St John’s wort in herbal preparations included in the Herbal Preparations Decree of the Dutch Commodities Act.
However, a warning on all products containing St John’s wort about possible interactions with medicines is now a legal requirement, after Bruno Bruins, Dutch Minister of Medical Care and Sport, addressed the issue in parliament back in 2018.
In that session, Bruin was responding to findings of a broadcast investigating the sale of St-John's wort products, where it questioned the preparations’ availability at chemist or health food stores.
“Users often seem to assume that using herbal preparations pose little or no risk because it involves natural products. But also, natural products can contain substances that have harmful effects on health.
“Like Radar’s broadcast shows, products containing St. John's wort are not only available as an herbal preparation, but sometimes also available as a herbal medicine.
“I think it is important for consumers who want a product with St. John's wort, be informed as well as possible about a possible interaction with certain drugs.
“Regardless of whether they buy this product as an herbal remedy or as an herbal preparation. I want therefore warning text on all products containing St. John's wort required by law set.
“I want to realise this before the end of this year on the basis of the Commodities Act. In addition, it is important that consumers notice any side effects and report interactions.”
Regarding herbal tea preparations, RIVM’s report admitted more information on the hypericin content of teas made from St John’s wort would be needed for a more reliable exposure estimate and to draw firmer conclusions.
“Given these concerns, RIVM advises consumers to be cautious with the use of herbal preparations containing St John’s wort, and to not use these supplements and herbal teas in combination with medicines.
“RIVM considers that these concerns cannot be covered with obliging warning phrases. Therefore, RIVM advises consumers to consider restricting the use of St John’s wort in herbal preparations by law,” the report added.
“Also, it is advised to consider which St John’s wort product should be regarded as medicines and consequently would require a premarket assessment on safety, efficacy and quality.”