It appears that cycling has a long history of doping. According to this Wikipedia article doping and cycling goes back to the 19th century.
* Arthur Linton from Aberdare in Wales died aged 24 of 'exhaustion and typhoid fever' a few weeks after finishing second in the Bordeaux-Paris race and a race at Catford. Linton was managed by the notorious Choppy Warburton,  whose success was questioned, with claims that he drugged his charges.  Jimmy Michael is said to have accused Warburton of poisoning him, before he was taken to court for libel.  Rudiger Rabenstein claims that Arthur Linton was "massively doped" for the 1896 Bordeaux-Paris.