I have just noticed this little program on BBC Radio 3 tonight (Saturday, 22:00-22:30 GMT). It is about a series of poisonings carried out by women in the village of Nagyrev in Hungary between 1914 and 1930. A midwife started supplying women with arsenic to solve their relationship problems but things got a bit out of hand. It has been estimated there were about 300 victims [but see comments]. More details here and here. I am surprised that this story hasn't yet been made into a film.