St. John's Wort is commonly used around the world to treat depression. There is some scientific evidence to support its use for mild to moderate depression but this remains controversial as there is also evidence that suggests it has no such effect. This herb is also known to increase the levels of cytochrome P450 enzymes and that can cause problems for other drugs.
Voriconazole (Vfend) is one of the newer antifungal drugs that is in use to treat aspergillosis. Its concentration in the blood is reduced by the action of cytochrome P450 enzymes, so an increase in the level of those enzymes will reduce the amount of voriconazole available to attack fungal growth:
In vitro studies have indicated that voriconazole is metabolized by the cytochrome P450 isoenzymes 2C19, 2C9, and 3A4. Because long-term use of St. John's Wort (a cytochrome P450 inducer) could lead to reduced voriconazole exposure, concomitant use of these drugs is contraindicated.If a patient is prescribed voriconazole it is therefore best if they do not take this herbal medication. The FDA in the US have required that a warning is added to Voriconazole medication prescribing information