Understanding drug interactions with St John's wort (Hypericum perforatum L.): impact of hyperforin content.

OBJECTIVE: The aim of this study was to review herb-drug interaction studies with St John's wort (Hypericum perforatum L.) with a focus on the hyperforin content of the extracts used in these studies.

METHODS: PUBMED was systematically searched to identify studies describing pharmacokinetic interactions involving St John's wort. Data on study design and the St John's wort extract or product were gathered to extract hyperforin content and daily dose used in interaction studies.

KEY FINDINGS: This analysis demonstrates that significant herb-drug interactions (resulting in a substantial change in systemic exposure) with St John's wort products were associated with hyperforin daily dosage. Products that had a daily dose of <1 mg hyperforin were less likely to be associated with major interaction for drugs that were CYP3A4 or p-glycoprotein substrates. Although a risk of interactions cannot be excluded even for low-dose hyperforin St. John's wort extracts, the use of products that result in a dose of not more than 1 mg hyperforin per day is recommended to minimise the risk of interactions.

CONCLUSIONS: This review highlights that the significance of herb-drug interactions with St John's wort is influenced by the nature of the herbal medicines product, particularly the hyperforin content.