Effect of goldenseal (Hydrastis canadensis) and kava kava (Piper methysticum) supplementation on digoxin pharmacokinetics in humans - Gurley, B J; Swain, A; Barone, G W; Williams, D K; Breen, P; Yates, C R; Stuart, L B; Hubbard, M A; Tong, Y; Cheboyina, S (Drug Metab Dispos, 2007)