The Tenth Doctor ejects cyanide in gas-like form. (TV: The Unicorn and the Wasp)
Cyanide was a white powder which was poisonous to many species. It killed by inhibiting cellular respiration. Symptoms included headache, nausea and convulsions. Cyanide poisoning could be reversed with ethylenediaminetetraacetic acid. (TV: Rendition)
The Birastrop were not affected by it. (TV: The Brain of Morbius)
In 1899, Dr. Tiberius Finch used capsules filled with cyanide to compel his Blowfish creations. (PROSE: The Baby Farmers)
In 1926, the Tenth Doctor was poisoned by Arnold Golightly with cyanide. Although by the time he noticed the symptoms of cyanide poisoning it would have been too late for a human to survive, the Doctor neutralised the poison by drinking ginger beer, eating walnuts for protein and anchovies for salt, and then getting a shock - a kiss from Donna Noble. This allowed him to eject the cyanide from his body through his mouth in a gaseous form. (TV: The Unicorn and the Wasp)
UNIT used cyanide gas to kill a swarm of giant cave insects. (PROSE: Caverns of Horror)
In 1984, Lt. Doyle attempted to kill the Sixth Doctor by giving him cyanide-laced coffee. (AUDIO: The Reaping)
In the 1980s, Oscar Botcherby used cyanide to kill moths for his collection, saying it was quicker and kinder to them than other poisons. The Sixth Doctor used Oscar's cyanide to smother and kill Shockeye of the Quawncing Grig. (TV: The Two Doctors)
The Fourth Doctor injected cyanide (in a gaseous form) into the laboratory of Mehendri Solon, killing him. Morbius survived as the body Solon had created for him included a set of lungs from a Birastrop. (TV: The Brain of Morbius)
The Fourth Doctor suggested using cyanide to kill the giant rats that inhabited the London sewers. (TV: The Talons of Weng-Chiang)
When forced to create EDTA to cure arsenic poisoning, Gwen Cooper used cyanide in the antidote. (TV: Rendition)