Didn’t know this was still done, or even illegal. 1800’s I know they used it, when morphine or cocaine were the only alternative PEDs (and cocaine wasn’t always easy to get).
The 1904 Olympics marathon winner was American Thomas Hicks. He doped using strychnine (rat poison).
Had the race been run under current rules, Hicks would also have been disqualified for using strychnine: his assistants had given him a dose of 1/60 of a grain (roughly 1 mg) of strychnine and some brandy because he was flagging badly during the race; the first dose of strychnine did not revive him for long, so he was given another. As a result, he collapsed after crossing the finishing line. Another dose might have been fatal. Strychnine is now forbidden for athletes.