Herbal extracts used for upper respiratory tract infections: are there clinically relevant interactions with the cytochrome P450 enzyme system?

The regulatory requirements for assessing potential interactions between herbal medicinal products and other medicines can cause specific, additional phytopharmaceutical problems. In this short review we assess the state of our knowledge for herbal extracts commonly used as over the counter (OTC) products for upper respiratory infections and which in many cases are considered to have immunomodulatory effects. Overall, the data on the safety of these products is still limited and only in the case of Echinacea preparations can preliminary conclusions be drawn. The available evidence points to weak cytochrome P450 inhibition which is unlikely to be of clinical relevance.