Barbiturates (derivatives of barbituric acid) were first introduced for medical use in the early 1900s. More than 2,500 barbiturates have been synthesized, and in the height of their popularity about 50 were marketed for human use. Today, only about a dozen are used. Barbiturates produce a wide spectrum of CNS depression, from mild sedation to coma, and have been used as sedatives, hypnotics, anesthetics and anticonvulsants.

The primary differences among many of these products are how fast they produce an effect and how long those effects last. Barbiturates are classified as ultrashort, short, intermediate and long-acting.

The ultrashort-acting barbiturates produce anesthesia within about one minute after intravenous administration. Those in current medical use are methohexital (Brevital), thiamylal (Surital) and thiopental (Pentothal).

Barbiturate abusers prefer the short-acting and intermediate-acting barbiturates pentobarbital (Nembutal), and secobarbital (Amytal). Other short- and intermediate-acting barbiturates are butalbital (Fiorinal, Fioricet), butabarbital (Butisol), talbutal (Lotusate) and aprobarbital (Alurate). After oral administration, the onset of action is from 15 to 40 minutes and the effects last up to 6 hours. These drugs are primarily used for sedation or to induce sleep. Veterinarians use pentobarbital for anesthesia and euthanasia.

Long-acting barbiturates include phenobarbital (Luminal) and mephobarbital (Mebaral). Effects of these drugs are realized in about one hour and last for about 12 hours, and are used primarily for daytime sedation and the treatment of seizure disorders or mild anxiety.