Ron, I am sure that plays a large part, but look at Cogane...it is plant based.
I think it may have to due with how volatile it is. Seems to inhibit or enhance drug metabolism, but I don't see how they could formulate something for us because think of how many differing interactions they would need to list. Way too much liability involved.

The compound that current researchers name responsible for the "grapefruit effect" is bergamottin, a plant compound that works in a plants defense as in having a bitter taste or toxic leaf. Just look at the root "bergamot"; this is what gives Earl Grey tea its heavenly scent and unusual taste. I am just wondering if a cup of Earl Grey may have a similar effect for some? It seems promising because it comes from the fruit of the plant so that bergamottin goes into the tea. Oh, and one citation it is neuroprotective.


Cell signaling pathways in the mechanisms of neuroprotection afforded by bergamot essential oil

Well, no grapefruit juice, but I will have a cup of Earl Grey in the morning...