Not to the best of my knowledge, the only evidence we have is SwissTemples' anecdotal report which isn't even sound because he is using a myriad of other treatments.
Notcoolanymore is actually right to post the David Tennant laughing GIF, since castor oil's effectiveness in regrowing hair in those with Androgenetic Alopecia is still just a theory, we have no clinical studies regarding its use in treating Androgenetic Alopecia. That being said, it is a good theory as PGE2 and similar compounds such as bimatoprost are reported to stimulate hair growth and castor oil activates 2 out of the 4 prostanoid receptors that PGE2 activates.
The logic behind the use of castor oil, besides its effectiveness in increasing PGE2 expression, is the fact that it's notoriously inexpensive. $10 AUD for a 473 mL bottle @ 1 mL orally per day will last you well over a year, it's a good deal for something that may very well be effective because it's easy to take and you don't have much to lose.
If you notice it has done nothing after that 1 year of use, oh well, you've only wasted $10. There certainly are worse experimental treatments for Androgenetic Alopecia.
