The Australian star, who plays police chief Steve McGarrett in the cop show reboot, has checked himself into rehab in order to wean himself off pain pills he has been taking following a recent shoulder injury.
He will take a break from the show to focus on his recovery, but is expected to rejoin the cast once his rehab stint is concluded.
O'Loughlin's representative tells Usmagazine.com, "Alex is taking a short break from Hawaii Five-0 to receive supervised treatment for prescription pain medication due to (his injury)."
A spokesman for his TV bosses reads, "We respect and support Alex's decision. Everyone at CBS Television Studios and Hawaii Five-0 wishes him well and we look forward to his return."