Choi Seung-hyun, also known as T.O.P of the Korean group Big Bang, was found unconscious Tuesday.
A report from The Korea Herald said Choi was rushed to the hospital due to an apparent drug overdose.
The incident occurred a day after Choi was indicted, without detention, on charges of smoking marijuana.
It was earlier reported that Choi was suspected of smoking marijuana four times with a female friend at his home in Seoul in October last year.
Choi has been serving his mandatory military service at the Gangnam Police Station in Seoul since February.
However, it was announced last Wednesday that he will be expelled from his division following his indictment.
The 29-year-old rapper initially denied smoking marijuana, but admitted to smoking marijuana twice after he tested positive for marijuana use.