Dennis Quaid says his "greatest mistake" was becoming addicted to cocaine.

The 57-year-old actor first started experimenting with the drug when he moved to Hollywood to try and make it as an actor in the early 1970s and, after becoming dependent on it, continued to use cocaine until the late '80s.

Now, decades later, he realises his behaviour was stupid and attributes his substance abuse with the massive changes that were happening in his life.

In an essay he wrote for Newsweek magazine, he revealed: "My greatest mistake was being addicted to cocaine. I started after I left college and came to Los Angeles in 1974. It was very casual at first. That's what people were doing when they were at parties . Coming from where I came from - from Houston into Hollywood - and all of a sudden this success starts happening to you, I just didn't know how to handle that. Doing blow just contributed to me not being able to handle the fame."

Dennis claims by the time he filmed 1987 movie 'The Big Easy' he was so hooked on cocaine he was getting "an hour of sleep a night" and admits it started to "affect" his acting.

The 'Soul Surfer' star - who was married to actress Meg Ryan while he was battling with his addiction - realised he had to get clean after his band The Eclectics split up following a concert at the China Club in Los Angeles.

He stated: "I had one of those white-light experiences that night where I kind of realised I was going to be dead in five years if I didn't change my ways."

Dennis - who fell off the wagon after his 1990 film 'Wilder Napalm' flopped at the box office - now believes his addiction has made him a better person.

The actor - who raises three-year-old twins, Thomas and Zoe, with his wife Kimberly - insisted: "That time in my life actually chiselled me into a person. It gave me the resolve and a resilience to persevere in life. If I hadn't gone through that period, I don't know if I'd still be acting. In the end, it taught me humility. I really learned to appreciate what I have in this life."