Board Thread:Theories and Speculation/@comment-45444155-20200728155230/@comment-3523655-20200801155121

Curse Mark basically hurts like hell, until you're used to it.

When you finally use it, it multiplies your chakra, then quickly drains it. So if you have no chakra when you enter the state, you might die.

Also, you go crazy, with time.

Chapter 66 - It's stated that the Curse Mark eats away at/erodes the user's body, and that if Sasuke uses it too much, he'd be dead.

Chappter 179 - The Sound Four tell Sasuke that the more he uses it, the crazier he gets, until he's so far gone that he's easily susceptible to Orochimaru.

Chapter 186 - The Sound Four state again that their energy drained too much from using the Curse's 2nd state, and were thus unable to use their bodies, and stressing that they were resting.