Cassil

Cassil was a shrub used by rich men as birth control.

Description
Cassil looked very similar to a simple mustard plant. The plant itself held little value, however, its seeds were gathered for their medicinal properties. Eating a little ground cassil seed rendered a man infertile and unable to propagate for a period of time from four to twelve days. On average, the medicine took effect within an hour. One dose of the herb cost a single gold coin. This effect was exclusive to humanoids.

Reputation
There were many tales of rulers being dosed by their disloyal courtiers with powdered cassil in order to end their family line.