To back up what CD is saying, I have read many, many (albeit anecdotal) reports from PFS guys stating that nettle was terrible for them/set them back considerably, etc... too many for it to be coincidence to my mind. I bought a bottle an age back and luckily read up on it first, so said bottle is now gathering dust somewhere. I too came across studies regarding it binding 5ar.
Again just theorising, but i wouldn't be surprised if nettle didn't harm me upon taking it at all if I had not done a lot of damage with much more potent finasteride, but now to add something like that to the mix would very much be playing with fire for a lot of us.