His condition is being monitored and more will be known in 24-48 hours.
Cousins spent Monday morning in the emergency department before he was sedated and moved to intensive care on Monday afternoon.
Richmond football manager Craig Cameron told the media the club doctor was contacted by Cousins' girlfriend when she had difficulty waking him on Monday morning.
“As you’re all probably aware Ben Cousins has had an adverse reaction to a sleeping pill,” Cameron said.
“This morning his girlfriend rang the club and spoke to the club doctor to let him know that she found it difficult to rouse him and it was decided to take him to Epworth hospital.
“The only information we have from the staff is that it was an adverse reaction to a sleeping pill and as I say we really won’t know more for the next day or so.”
Cameron was unaware of exactly how many sleeping tablets Cousins had consumed last night but denied the incident was suspicious.
“We’ve got no suspicion that there was anything illicit involved,” Cameron said.
“It’s definitely concerning for his health. He’s in hospital in intensive care. His condition won’t be known for another 24 hours and that’s concerning for sure and we’re worried about Ben’s health.”
Cameron admitted he wasn’t previously aware that Cousins was taking a sedative but dismissed it as being unusual.
“He probably takes one after a game I’d imagine to try and calm down and sleep. I don’t think it’s unusual for players to take sedatives or sleeping tables after games.”
Cameron said Monday's issue was unrelated to an abdominal complaint Cousins suffered earlier this year.
Cousins, who played in the 2006 premiership as part of his 238 games for West Coast, was sacked by the club in 2007 after his arrest on drugs charges - later dropped - and spent 2008 out of the game after being deregistered by the AFL.
He was picked up by the Tigers with the last pick in the 2009 NAB AFL Pre-Season Draft, and despite battling injury, has played 25 matches for his new club.
