Horace Wells:

Pioneered the use of anesthesia in the 1840s

How he died: Used anesthetics to commit suicide

While experimenting with various gases during his anesthesia research,
Wells became addicted to chloroform. In 1848 he was arrested for spraying
two women with sulfuric acid. In a letter he wrote from jail, he blamed
chloroform for his problems, claiming that he'd gotten high before the
attack. Four days later he was found dead in his cell. He'd anaesthetized
himself with chloroform and slashed open his thigh with a razor.