- "My purpose, is to teach you."
Brainwashing is a method used by one power to coerce, influence, or "teach" their subjects/victims into pledging his or her allegiance to them. The Goa'uld and Wraith often commit to brainwashing. However, Bra'tac claims to be able to sense whether or not someone was brainwashed, not through technology, just by looking into his or her eyes.
One of the first notable brainwashing techniques first encountered by the Stargate Program was in 1997, when the Goa'uld Queen Hathor used a pink gaseous agent in her breath to influence the Stargate Command personnel into falling into her whim. The effects wore off after she gated to Chulak. (SG1: "Hathor")
In 1998, Apophis brainwashed Teal'c's son, Rya'c. He was primarily brainwashed with the purpose to lure SG-1 to rescue him and send him to Earth. Apophis coerced Rya'c into releasing a highly dangerous bio weapon implanted in his teeth to spread across the planet and kill all 6 billion Tau'ri. Fortunately, they caught Rya'c on his mission just in time, and his mind became free after Teal'c shot him with a Zat'nik'tel, neutralising the hold Apophis had on him. (SG1: "Family")
The Goa'uld Setesh, who hid on Earth for millennia, used Nish'ta, a substance stronger than Hathor's breath to brainwash humans into joining his group, the Cult of Setesh. In 1999, SG-1 were temporarily brainwashed by the Nish'ta, but the brainwashing was broken through a similar method Teal'c used on Rya'c, by introducing an electric shock through concealed earpieces, the shock throwing off the Nish'ta after it had settled into their systems following an hour's exposure. They then broke all members of the cult by shooting them once with Zats. (SG1: "Seth")
A Za'tarc is a being who has been mentally reprogrammed to, when exposed to a trigger, assassinate another being and then kill themselves. The method of brainwashing was not explained. This method of brainwashing can be detected by using a Za'tarc detector, which forces a person to relive their memories through questioning to determine if there is anything that they are concealing from themselves, thus alerting them to the possibility that someone has fallen under the influence of a Za'tarc. (SG1: "Divide and Conquer", "Allegiance")
In 2001, Teal'c was killed on Vorash, and transported to Apophis' mothership by his Jaffa. Apophis proceeded to revive, and brainwash, Teal'c into believing he was Apophis's First Prime again. After SG-1 eventually captured Teal'c, they attempted to break the brainwashing. This attempt failed. Bra'tac resorted to confiscating Junior, so Teal'c would undergo the Rite of M'al Sharran, forcing Teal'c to relive his past in the hopes that it would help Teal'c re-trace the steps that lead to him realising that the Goa'uld were not gods. Fortunately, that method freed his mind, and he pledged his allegiance to the Tau'ri once again. (SG1: "Exodus", "Enemies", "Threshold")
In 2006, Ba'al captured several members of the Free Jaffa Nation and brainwashed them into joining him. One of the Jaffa was Maz'rai who used the Rite of M'al Sharran to try to break the brainwashing. While he apparently succeeded, he didn't survive the effort but left a clue that led to the discovery of the truth. One of the victims was Teal'c, who was able to break the brainwashing himself. After he killed one of the Ba'al clones, Teal'c told Lt. Colonel Cameron Mitchell that to resist the influence of others, knowledge of oneself is most important. Afterwards, Teal'c and Bra'tac helped the other Jaffa break the brainwashing. (SG1: "Stronghold")
In 2007, Ba'al, presumably through The Trust, brainwashed NID Agent Malcolm Barrett so he could break out in his infiltration of the SGC. It worked, but afterwards the SGC realized the truth and helped Barrett break the brainwashing. (SG1: "Insiders", "Uninvited")
In 2009, the Lucian Alliance, presumably through leftover Goa'uld technology, brainwashed Colonel David Telford into becoming an agent for them. His brainwashing was broken when he was suffocated to death in Dr. Nicholas Rush's body by Colonel Everett Young and then revived. Immediately recovering from the brainwashing, Telford regained his loyalty to the Tau'ri and his sense of morality and confessed to doing terrible things which he regretted deeply. Telford still possessed all his memories of being under Alliance control and used his knowledge to convince them that he was still on the Alliance's side during the Lucian Alliance invasion of Destiny. (SGU: "Subversion", "Incursion, Part 1")
In Pegasus, the Wraith commit to brainwashing through different methods; they often feed on their victims and restore their life force until they were coerced via the Wraith enzyme in the system. Some of the notable victims include Satedans Ara, Hemi, Marika, Rakai, Tyre, and Ronon Dex. Hemi and Marika were killed due to the physical stresses of the process, while Tyre and Dex broke their brainwashing by going into withdrawal from the enzyme. (ATL: "Reunion", "Broken Ties")