"He realised he needed help and is committed to his sobriety," a source told US Weekly.
The news comes after Josh said he was giving up alcohol completely after becoming embroiled in two fights over the same weekend earlier this month.
The talented 45-year-old actor was caught on camera in a tussle at an Irish pub in Santa Monica on 2 November. The previous evening, he was filmed getting into a verbal altercation with a cab driver at a Los Angeles drive-thru.
On Monday 4 November, he told TMZ that he was stopping drinking for good.
When asked if he regretted the incidents from the weekend, the No Country for Old Men star said, "Absolutely. It won't be happening again… That's it. Completely done."
It has been a difficult year for Josh. In February, he and his wife Diane Lane announced they were divorcing after eight years of marriage.
"They've been separated for several months. This was a hard decision for both of them to make," a source close to the pair told People. "The relationship just ran its course.
The couple, who were married in a 2004 ceremony at Josh's California ranch, were first introduced by the actor's stepmother Barbra Streisand at a party in 2002.
Josh's father, James Brolin, said in February that his son was doing well following the split.
"He's great," said the 73-year-old actor, who has been married to Barbra since 1998. "You know, everything is mutual. It's all okay."