Los Angeles - Matthew Perry admits getting sober was "really hard".
The former Friends actor - who went to rehab for Vicodin addiction in 1997 and again for alcohol and prescription drug problems in 2001 - was always aware that getting his struggles under control would take a long time.
He said in a video by The Hollywood Reporter: "You can't have a drug problem for 30 years and then expect to have it be solved in 28 days."
Going on to praise treatment centres such as Los Angeles' Phoenix House, he added: "I was very moved by the hope that I saw there, which is what this is all about. Getting sober is a really hard thing to do."
And the 46-year-old star admitted having to go through his addiction in the public eye made things even more difficult.
He said "I'm a pretty private person, but I was on a TV show that 30 million people were watching. So people knew. It was so public what was happening to me."
In the video, the Odd Couple actor met with three other clients at the Phoenix House facility and stressed the importance of turning focus away from yourself to help others.
He said: "Treatment centers are important because they sort of separate the addict from their environment where they were using.
"The most important thing is to get outside of your head and help another person."