Felblood (aka fel blood) is a term that refers to demonic blood. Felblood is highly addictive as well as corruptive. Demons sometimes tempt spellcasters by offering small amounts of their blood in exchange for services. ( The blood of the demon )Mannoroth was offered to the orcs. It empowered them and corrupted them, and they became addicted that power. Further felblood corruption from Mannoroth created the chaos orcs and fel orcs. Orcs suffered withdrawal symptoms after the second war known as lethargy. Elves that have become corrupted by drinking felblood are known as the Felblood, the felblood elves.
Even felblood that is old and diluted still possesses tremendous power. The Pools of Aggonar were once a sacred site to the draenei their waters were corrupted after the blood of the demon Aggonar was spilled into them, and the blood still empowers or corrupts creatures near it. The terrorfiends in the area are empowered by the pure demonic energies of the original blood.
Anyone who drinks felblood has a chance of becoming dependent on felblood, and unless the person continues to drink it daily, he will suffer withdrawal symptoms. He has a chance of breaking the addiction seven days after first drinking the felblood. ( )