Venom

Venom is natural toxin secreted by animals. Venomous animals on Earth include species of snakes, arachnids, and insects.

A mugato's fangs contain venom that attacks its prey's nervous system, killing it after a few hours. Mahko root is the only known antidote. 

Lieutenant Worf, suffering from Barclay's Protomorphosis Syndrome in 2370, developed a venom sac beneath his jawline and began spitting the acidic compound throughout the USS Enterprise (NCC-1701-D). When Dr. Crusher discovered the sac on his neck, Worf spit the venom in her face, severely disfiguring her. He later attacked Captain Picard in the same fashion. 

The venom of Regalian fleaspiders can improve a humanoid's blood circulation.