Hypnosis was a psychological technique. It produced a trance-like state in which one was relaxed and more susceptible to suggestion. One who hypnotizes was called a hypnotist.
In 2270, Leonard McCoy performed hypnosis on Pavel Chekov as a means to help him imagine being Harry Mudd, to help track down Mudd's Superstella. McCoy was uneasy tampering with the officer's inhibitions, but Chekov said he trusted the doctor not to harm him. It worked – Chekov suggested the planet Sarai, and Mudd was located in that sector. (TOS - Mudd's Angels short story: "The Business, As Usual, During Altercations")
In February 2274, Captain Morgan Avery suspected that the armed mobilization of Husians on Hus-24 against Starfleet was a result of hypnotism by their spiritual leader, Edrem. (TOS comic: "Husian Gambit")
In 2285, hypnosis by Dr. Krista Sivertsen was unable to reveal to James T. Kirk why he thought he was a participant in the events recounted in the novel Strangers from the Sky. (TOS novel: Strangers from the Sky)
In 2375, Beverly Crusher used hypnotism to treat Colin Blakeney's temporal shock. Hypnosis allowed Blakeney to accept Data, Deanna Troi and Crusher as participants in holodeck simulations of his past, in order to help him reintegrate his memories. (TNG comic: "Forgiveness")
While he was in stasis, 20th century Doctor Alfred Bleikoff was surgically altered: his brain was replaced with an electronic brain capable of generating a mass hypnotic effect. In 2266, after he was revived and returned to Earth, Bleikoff used the technique to try to remove the Earth defense screen, likely in order to facilitate an invasion. (TOS comic: "Prophet of Peace")
Spock and Leonard McCoy attempted unsuccessfully to hypnotize the crew of a threatening Vinithi ship by modifying a sonic hypnosis-inducer to affect their physiology. (TOS novel: The Three-Minute Universe)
In 2267, Kor thought that the Organian phenomena of weapons radiating at high temperatures was an affect of hypnosis. In 2269, Spock theorized that Organians were expert hypnotists, and what they'd perceived on Organia was a result of hypnotism rather than reality. (TOS - Star Trek 2 novelization: Errand of Mercy, TOS novel: Spock Must Die!)
In the 2260s, after being knocked out by small drones, James T. Kirk awoke apparently hypnotized. He walked into a cave and climbed into a stasis chamber as if he were in a trance. (TOS comic: "Rescue at Raylo")
In 2267, a hypnotic Siren song was heard by James T. Kirk. He lashed himself to the mast of a Homeric ship the way Ulysses did thousands of years ago, in order to hear the song without obeying its hypnotic message to commit suicide. (TOS comic: "What Fools These Mortals Be..")
Klingon Professor Karkax used a mechano-hypnotiser to perform mass hypnosis on the Lothorian administration, then on the crew of the USS Enterprise. They were ordered to crash the starship into the capital of the Federation, and the ploy would have succeeded except that Spock's Vulcan physiology was able to overcome the hypnotism. (TOS comic: "By Order of the Empire")
- Alfred Bleikoff (altered)
- Beverly Crusher
- Edrem (possibly)
- M-113 creature
- Leonard McCoy
- Rigelian hypnoid
- Rycho (possibly)
- Krista Sivertsen
- Starfleet Academy (Priam IV test)
- Deanna Troi
- Carl Wentworth
- alpha hypnotape
- Andronican mind-control
- sodium pentathol
- sonic hypnosis-inducer
- Venus drug
- TOS episode & Star Trek 6 novelization: The Man Trap
- TOS episode & Star Trek 10 novelization: A Private Little War
- TOS episode & Star Trek 8 novelization: Catspaw
- TNG episode: "Lonely Among Us"
- VOY episode: "Spirit Folk"
- TOS - Star Trek 2 novelization: Errand of Mercy
- TOS - Star Trek 5 novelization: Whom Gods Destroy
- TOS novel: Planet of Judgment
- TOS - Mudd's Angels short story: "The Business, As Usual, During Altercations"
- TOS novel: The Prometheus Design
- TOS novel: Mutiny on the Enterprise
- TOS novel: Demons
- TOS novel: Dreams of the Raven
- TOS novel: Strangers from the Sky
- TOS novel: The Three-Minute Universe
- TOS novel: The Cry of the Onlies
- TOS novel: Crossroad
- TOS novel: The Joy Machine
- TOS - Vulcan's Soul novel: Exodus
- TOS comic: "By Order of the Empire"
- TOS comic: "Rescue at Raylo"
- TOS comic: "Prophet of Peace"
- TOS comic: "What Fools These Mortals Be.."
- TOS comic: "Husian Gambit"
- TNG novel: Survivors
- TNG - A Time to... novel: A Time to Die
- TNG comic: "I Have Heard the Mermaids Singing"
- TNG comic: "Forgiveness"
- DS9 novelization: Emissary
- VOY novel: Cybersong
- VOY novel: Battle Lines
- TLE novel: Deny Thy Father