Deryck Whibley has posted on his website that he has been sick for the past few weeks, including spending a month in hospital.
He says it's because of the "hard boozing" he has been doing over the years.
Whibley says he was at home one night about a month ago when he collapsed, falling to the ground unconscious.
Whibley, who was once married to singer Avril Lavigne, says his liver and kidneys "collapsed."
He says the health crisis has forced him to make drastic lifestyle changes.
"Needless to say it scared me straight," he said in the posting that is dated May 16.
"I finally realized I can’t drink anymore. If I have one drink the docs say I will die."
There is one positive thing that has emerged from his health problems, Whibley said.
"I have my passion and inspiration back for writing music," he writes.
"I already have a few song ideas for new songs. Soon it will be time to start making an album and getting back to touring again."
Sum 41 was formed in 1996. The Ajax, Ont., band has sold more than 30 million albums worldwide and has won two Junos.