A sedative was a drug used to calm down a patient or to induce sleep.
Sedatives were often administered with a hypospray in a dosage of usually not more than several ccs.
Aldebaran mud leeches could be used to treat insomnia as their secretions acted as a natural sedative. (ENT: "Anomaly")
Captain Picard's aunt Adele's recipe for a warm milk toddy was working perfectly as a natural sedative, as the heat activated amino acids in the lactose and it also tasted delicious. (TNG: "Schisms")
Constable Odo told the Rakhari criminal Croden he would sedate him if he would not be quiet during their trip to Rakhar. (DS9: "Vortex")
Makara herbs could act as an antidote to sedatives. While taking these herbs during her pregnancy, Major Kira Nerys was able to overpower Silaran Prin by pretending the sedatives he gave her worked. (DS9: "The Darkness and the Light")