Just read that some study indicated that the efficacy of an oral drug is reduced when taken with grapefruit juice, and orange and apple juice as well. I don't know the science behind it but i just thought I'd pass it along, in case you were popping your propecia with a glass of OJ in the morning. I was.
Maybe now I can go to every other day dosage with water and get the same benefits as every day with OJ....until some study comes along to indicate water is bad for you now.

interesting find. the problem is with something called naringin.
http://en.wikipedia.org/wiki/Naringin
http://www.rspharmchem.com/naringin.htm
according to the 2nd link, it can only increase absorbtion. as the op mentioned though, it's if you drink juice with the meds which for me is fine since i take finasteride before i go to bed.