Ok, so I went for an over the top title. Seriously- this new peer-reviewed report looks at how certain fruits and vegatables can affect pharmacokinetics.
A quote from the article-
"As little as 6.0 oz of grapefruit juice may lower the amount of a drug needed to produce the desired effect, which could cause an overdose. The blood that absorbs nutrients passes through the liver before reaching the general circulatory system (the first-pass). The ability of a drug to successfully pass from the GI tract to the plasma is called its bioavailability. Grapefruit juice inhibits first-pass drug metabolism, increasing bioavailability."
I remember reading something about grapefruit juice years ago, this provides a lot more info.