St John's wort (Hypericum perforatum) has been found, on average, to decrease the maximum
serum concentration of
tacrolimus by 65% and the AUC by 32%. However, the decrease in AUC ranged from 15% to 64%, with one patient having a 31% increase in AUC.
Given the unpredictability of the interaction (and the variability in content of St John's wort products) it would seem prudent to avoid St John's wort in transplant patients, and possibly patients taking
tacrolimus for other indications. If St John's wort is withdrawn monitor
tacrolimus levels and adjust the dose accordingly.