Porter told the Associated Press that during the winter of 1979-1980, he became paranoid, convinced that baseball commissionerBowie Kuhn, known to be tough on drug use, knew about his drug abuse, was trying to sneak into his house, and planned to ban him from baseball for life. Porter found himself sitting up at night in the dark watching out the front window, waiting for Kuhn to approach, clutching billiard balls and a shotgun.
During spring training in 1980, former Los Angeles Dodgers pitcher Don Newcombe paid a visit to the Kansas City clubhouse. He asked the players 10 questions, the point of which being if a player answered three or more of the questions with an affirmation, the player might have a problem with drugs or alcohol. Porter affirmed all 10 questions and checked himself into a rehabilitation center, admitting he had abused alcohol, cocaine, Quaaludes, and marijuana.
Over 17 Major League seasons, Porter had a career batting average of .247 and an on-base percentage of .354 with 188 home runs, 826 RBIs and a .982 fielding percentage. As of the 2009 season, he ranked 21st on the all-time list for home runs by a catcher, ranked as only player to bat with one hand, and 20th for RBIs by a catcher. Porter caught two no-hitters during his career (Jim Colborn in 1977, Bob Forsch's second career no-hitter in 1983). Porter was also notable for being one of the few Major League catchers of his time to wear eyeglasses behind the plate, at a time when most players needing vision correction were using contact lenses.
Porter was married twice. His first marriage, to the former Teri Brown in 1972, ended in divorce in 1976. On November 29, 1980, he married Deanne Gaulter, who survived him in death. The couple had three children: Lindsey, Jeffrey, and Ryan.
In 1984, Porter wrote an autobiography titled Snap Me Perfect!, in which he detailed his life in baseball and his struggles with substance abuse.
Porter dabbled in broadcasting late in his life, and also in the antique business on and off during his post-baseball years. But on August 5, 2002, he left home, saying he was going to buy a newspaper and go to the park. He was found dead in Sugar Creek, Missouri, outside his vehicle that evening. An autopsy said he had died of "toxic effects of cocaine;" the level of cocaine in his system, consistent with recreational use, induced a condition called excited delirium that caused his heart to stop. Police theorize that Porter's car went off a road and got caught on a tree stump in La Benite Park in Sugar Creek, a Kansas City suburb. He got out of the car, walked to the nearby Missouri River and then back to his car. Authorities had initially speculated that he overheated while trying to push the car off the stump in high heat and humidity. But there was no evidence to indicate that he tried to move the car. The exact scenario at his death site is still unknown.