Does Ketoconazole shampoo definitely reduce DH in the scalp?

[bluestar99]

Is it true there was only one study that showed that Ketoconazole blocked DHT in the scalp. There doesn't seem to be a total consensus that it actually does do anything or even block DHT in the scalp.

And then if one only uses it out of shampoo how is it going to keep the DHT levels down days after the shampoo application?