Bailey serendipitously discovered that grapefruit increased levels of the antihypertensive drug felodipine in his own body in 1987, information which was pretty much ignored until he published a research paper in the Lancet in 1991 showing a doubling of felodipine levels in 6 volunteers who consumed grapefruit.Since then studies have shown that grapefruit juice acts by reducing presystemic felodipine metabolism through selective post-translational down regulation of cytochrome P450 3A4 (CYP3A4) expression in the intestinal wall.