Daredevil turned drug addict
Action star Wallace Reid was well-known for doing his own stunts, but this all changed on the set of The Valley of the Giant. Reid suffered an accident while filming in 1919 that led to a morphine addiction.
Any sort of rehab was too scandalous for his reputation to endure at the time, so the studio swept his substance abuse under the rug. Eventually it got so bad that they sent him to a sanitarium, but Reid was too far gone and died of a heart attack from withdrawal.