"one way out of an unhappy marriage in cultures where divorce was unavailable to wives"

I didn't realize that in a former life the great sci-fi novelist Charless Stross was a pharmacist, ahem, aher, a chemist since he's British.  And he took the time to write a really nifty piece on literary poisoning:

"Poisoning somebody is a violent assault, but a stealthy one: unlike shooting, stabbing, or punching it may not be obvious who's responsible, or even that an attack has taken place until much later. Historically it's often been a tool used by the weak against the overbearingly strong: one way out of an unhappy marriage in cultures where divorce was unavailable to wives. But, despite being stealthy, poisoning is also risky. Many legal systems punish poisoners more harshly than other murderers, either because it's the preferred tool of the oppressed against their privileged oppressor, or because it levels the playing field of violence between the weak and the well-armed and the latter don't like the taste of their own medicine.

So, before using poison in fiction, you need to be very clear about the motivation and expectancy of survival of the poisoner."

Absolutely do read the whole thing.