Sleeping gas

Sleeping gas was an anaesthetic used to incapacitate its subject.

After the Third Doctor stole the dematerialisation circuit from his TARDIS, the Master installed an alarm system that triggered the release of sleeping gas into his console room. It was activated by Jo Grant resulting in the incapacitation of both her and the Doctor. The Master was able to revive them though the use of an oxygen mask.

Later, having been captured by the Uxarieans, the Master used a handheld satchel of the gas to knockout his captives, allowing him and the Doctor to flee. (TV: Colony is Space)