EXCLUSIVE

9:43 AM PT -- Jim Carrey released a statement -- "I am shocked and deeply saddened by the passing of my sweet Cathriona. She was a truly kind and delicate Irish flower, too sensitive for this soil, to whom loving and being loved was all that sparkled. My heart goes out to her family and friends and to everyone who loved and cared about her. We have all been hit with a lightning bolt."

Jim Carrey's on-again/off-again 28-year-old girlfriend has committed suicide ... TMZ has learned.

Law enforcement tells TMZ, LAPD responded to a call in the L.A. area Monday night. We're told they went to a residence and found the body of Cathriona White.

Our sources say White left a suicide note addressed to Carrey which references their break up on Sept. 24. Cathriona tweeted on the 24th ... "Signing off Twitter, I hope I have been a light to my nearest and dearest."

Law enforcement tells us they believe she died from an overdose of drugs -- pills were next to her body. We're told 2 friends found Cathriona last night when they went to check on her.

53-year-old Carrey and White met in 2012, dated a few months and then split. They rekindled their relationship in May.