Similar to the Breath of Hathor, nish'ta is a biological compound employed by the Goa'uld as a powerful form of mind-control. Nish'ta is an organism delivered in a gaseous form and is absorbed by the body's tissues, rendering the subject's mind "extremely pliable" and open to suggestion.
An electrical shock, such as that delivered by a zat gun discharge, will kill the organism and free the victim from its control. Once freed, the subject is immune from repeat infection.
Family - Apophis uses a mind-controlling agent, which Teal'c later identifies as nish'ta, to brain-wash Teal'c's son Rya'c and turn him against his father.
Seth - SG-1 infiltrates the Goa'uld Seth's compound on Earth, where he uses nish'ta to control his "followers" -- including Jack, Sam and Daniel.