A cyanide pill is a pill, capsule, ampoule or tablet containing a fatally poisonous substance that a person ingests deliberately in order to quickly commit suicide. Military and espionage organizations have provided their agents in danger of being captured by the enemy with suicide pills and devices which can be used in order to avoid an imminent and far more unpleasant death
Cyanide is known as a highly toxic chemical, and can certainly cause death at the right concentrations. However, purchasing it is nigh on impossible, although on the Peaceful Pill Handbook forum (for PPH members only) there was one report of it being sold from China. It is possible to manufacture it, although not easily. In The Peaceful Pill Handbook1 there is detailed information on how to manufacture sodium cyanide. There are also a few articles that can be found searching on the web, although less detailed.
Manufacturing sodium cyanide requires extreme care, and it is certainly not recommended using the manufactured product without testing it first for lethality, otherwise the results could be extremely painful.
It is also possible to combine sodium cyanide with concentrated hydrochloric acid to create hydrogen cyanide gas that can be lethal in an enclosed space, and this method has been used in gas chambers over the years.