09-11-2014, 07:04 AM
It's likely from grapefruit's naringenin inhibiting the liver's CYP1A2 enzyme. Wikipedia has a list of things that CYP1A2 degrades and estradiol is on the list. PM's miroestrol is similar to estradiol so it probably gets hit by that enzyme too.
Turmeric is also on the inhibitor list, so it could be an alternative to grapefruit juice.
Turmeric is also on the inhibitor list, so it could be an alternative to grapefruit juice.