Truth Serum, or Truth Drug, a term applied to certain barbiturates that in some cases will compel the person to whom they have been administered to answer questions truthfully. Because the drugs do not consistently compel truthfulness, they are not an infallible means of extracting accurate information. Under certain circumstances, however, evidence or information obtained with truth serums may be admissible in courts.

Among the drugs used as truth serums are Amytal (a trade name for amobarbital) and sodium pentothal. These drugs, which are used in medicine as sedatives, act as depressants on the central nervous system and bring on a state of complete relaxation and a feeling of well-being.

Truth serums are also used in psychiatry to help patients speak more freely during psychoanalysis because they help the patient release many thoughts locked in the subconscious.