If the poison doesn't get renewed expires after 3 rounds.

Btw, seems to me right to add that the way poison tai works since 5.0 onwards is different than how if worked before 5.0, so if people is looking for old references to it they may go tru misunderstanding.

Before 5.0 poison tai stacks weren't increased by the same combo chase, so, in the case angelx showed you about madara and jonin minato you used to actually get 1 stack only by the whole combo chase, king of hell eventually included. Only different hits at that time added stacks, but, on the other hand, differently from now, at that time mystery skills added poison also if the skill was dodged, while now this doesn't happen anymore.

I hope i cleared some eventual misunderstanding that people would incur in.