Cp-191 is a hibernation drug originally developed for a manned Mars investigation project that never got anywhere. The drug is powerful enough to put a grown man to sleep for three months. It also allows for the brain's signals to become too flat, preventing anyone from waking up the person who ingests the drug, as well as use mind-related espers from poking around the ingester's brain.
It is used by Matsusada after realizing that he might be already affected by Agitate Halation, putting him to sleep, much to the inconvenience of Yomikawa Aiho and Stephanie Gorgeouspalace, who were trying to capture him.
- ↑ 1.0 1.1 Shinyaku Toaru Majutsu no Index Light Novel Volume 07 Between the Lines 1