From A Wiki of Ice and Fire
Widow's blood is a poison. It is named so for its color. It shuts down the bladder and bowels until the person dies from the body's own poisons.
A Clash of Kings
Tyrion Lannister sees widow's blood in Grand Maester Pycelle's collection of medicines and poisons.
A Storm of Swords
During Tyrion Lannister's trial for the presumed murder of King Joffrey Baratheon, Grand Maester Pycelle testifies that Tyrion had stolen several substances of his, including widow's blood, although Pycelle confirms that Joffrey's death was not due to it.
- ↑ 1.0 1.1 A Storm of Swords, Chapter 66, Tyrion IX.
- ↑ A Clash of Kings, Chapter 17, Tyrion IV.