'Eight Is Enough' Star Adam Rich Dead at 54

Adam Rich, who starred in the enormous hit, "Eight Is Enough" has died ... TMZ has learned.

A family member tells TMZ ... Adam died Saturday at his L.A. area home. The family member would not reveal the cause of death, but a law enforcement source tells TMZ someone came to his home and found him lifeless. The law enforcement source adds ... this was not foul play.

Adam played Nicholas Bradford, the youngest son on "Eight Is Enough." The series ran from 1977-1981.

He had other credits as well, including "Code Red" in 1981 and "Dungeons & Dragons" in 1983.

Adam made VH1's list of the greatest 100 kid stars, coming in at #73.

He retreated from show business in the '80s because he said he did not like the glare of the spotlight or, for that matter, anything celebrity-related.

Adam took up acting at Chatsworth High School in the San Fernando Valley. His drama teacher also taught Kevin Spacey, Val Kilmer and other big actors.

Sadly, Adam had substance abuse issues, which resulted in a 1991 arrest after he smashed a pharmacy window in an effort to obtain drugs. He was bailed out by Dick Van Patten, his TV dad on "Eight Is Enough." He had other legal issues as well.

Adam's mantra -- "Life is for living, and I live my life to the fullest every day."