I've just been re-reading The Poison Principle by Australian pharmacist and writer Gail Bell. It's an enjoyable cross-genre book starting from a family mystery - Bell's grandfather was accused of poisoning two of his young sons with strychnine - and she uses her investigation of this as the core of a wide-ranging exploration of the science, history, mythology and cultural impact of poisons and poisoners.
Another good book in this territory is Professor Andy Meharg's Venomous Earth, a "scientific, cultural and political history of arsenic", whose varied topics include the Madeleine Smith case, William Morris wallpapers, the Scottish prejudice against green sweets (down to 19th century Greenock traders' use of Scheele's Green - copper arsenite - as a food dye in confectionery "for the bairnies"), and arsenic's continuing significance in regions such as Bangladesh where tube well projects to provide cleaner water have exposed large populations to a different health risk, arsenic-contaminated groundwater.
Arsenic - 'the king of poisons' - is rich in historical interest. It's a well-trodden theory that Napoleon may have been a victim of 'Gosio gas' (the result of volatilisation of arsenical pigments in wallpaper by microbial methylation). But as "Was Napoleon a junkie?" mentions, arsenic was also taken deliberately for its stimulant properties, as famously used by Arsenic Eaters of Styria, 19th century Austrian peasants who habitually ate, as a tonic, normally lethal doses of arsenic. James Maybrick, Jack the Ripper suspect, was an arsenic addict, a fact that led to the almost certainly wrongful conviction of his wife for his murder by arsenic. Because of its ready availability, arsenic was popular with Victorian poisoners, and also caused some spectacular accidental mass poisonings, notably the Bradford Poisoning.