Board Thread:Theories and Speculation/@comment-5273810-20150207055437/@comment-5936871-20150406211933

I thought it was pretty obvious that it was because of Hashirama's cells. It's already been stated that Senju DNA enhances the power of the Sharingan. Half of Obito's body was made of Hashirama's cells and his MS was able to be used almost all the time for years without any drawbacks. Also look at Danzo, he had Hashirama's cells too and he was able to wield multiple sharingan as well as Shisui's mangeyko for who knows how long without any drawbacks as well. Although not confirmed, I believe it is pretty logical to assume it was because of Hashirama's cells.