The goal of the study is to examine the difference of the pharmacokinetics of metformin with
and without a 3 weeks pretreatment of St John's Wort. Furthermore secondary objectives
include changes in GLP-1, C-peptide, serum-insulin and plasma-glucose during an oral glucose
tolerance test, changes in OCT1 mRNA in plasma and changes in leptin and lipid-profile
following this possible interaction.