After throwing and detonating, the Hallucigen gas grenade will emit a green gas that distorts vision. It will cause NPCs to frenzy and begin to attack each other, regardless of whether or not they are attacking their own allies.
This crafting recipe will only appear with a HalluciGen gas canister in the inventory. One does not need the Demolition Expert perk to make these.
HalluciGen gas grenades are not randomly generated as loot. Instead, the HalluciGen gas canisters the Sole Survivor needs to craft at a chemistry station can only be found at HalluciGen, Inc., and are at a finite number of nine.
Some enemies are unaffected by the gas, as the game will indicate with a "<Name> is too powerful for this effect" notification.