Hypno-Gems are special crystals crafted out of raw Thrallium which emit a mind-altering form of otherwise harmless radiation. The recognizable green light renders those in its vicinity under a state of deep suggestibility. A skilled hypnotist or therapist can use Hypno-Gems to gently guide subjects into an extremely deep trance.

The villain Professor Spellbinder used Hypno-Gems to control a small group of coeds in the Sigma Somno Epsilon sorority at Metrobay University, using them to rob jewelry stores and banks.

Hypno-Gems can be worn decoratively and adhere to the body with limited assistance. It is thought that reknowned therapist Ella Mesmer uses a Hypno-Gem in her favorite pendant to expedite trance sessions with her patients.

It is implied that several mind-altering machines may utilize Hypno-Gems or Thrallium crystals to assist in controlling the minds of its victims, including H.E.R.-TV sets, H.E.R. rayguns, and even androids like MilkMaid and Sentius.