In the case of Hawley Crippen, the unusual poison choice, Hyoscine, led investigators to question the validity of the remains. It seemed unusual for the toxicologist to check immediately for the common alkaloids before looking for more common poisons. But what are the more common poisons used in murders?

As far as the murder of individuals is concerned there are relatively few agents that have been used and of course there is no way of knowing how many people have been deliberately killed this way because no doubt many such deaths were attributed to natural causes.

Mithridatism is the practice of protecting oneself against a poison by gradually self-administering non-lethal amounts. The word is derived from Mithridates VI, the King of Pontus, who so feared being poisoned that he regularly ingested small doses, aiming to develop immunity.