ADTH is a stimulant which can be dispersed through a starship's life support systems.
In 2367, Lieutenant Commander Data put 5 parts per million of ADTH into the airflow of the USS Enterprise-D to wake the crew after they had been stunned by the Paxans' fake wormhole. (TNG: "Clues")
Italic text Probably less of a stimulant then an aerosol chemical that is metabolised into a nuero-transmitor (?) that, once comming into contact with the brain, relays the message to the brain to wake up the body.