Depressant drugs effects on the brain can be summed up as decreased neural activity. In low doses for daytime use, these drugs may be prescribed to reduce anxiety (as sedatives) At higher doses many of the same drugs are prescribed as sleeping pills (hypnotics) These are referred to as sedative-hypnotics, part of the larger group of substances considered to be cns depressants. Alcohol is the most widely used depressant. Most widely prescribed types of sedative-hypnotics fall into the chemical grouping called the benzodiazepines, which largely replaced the barbiturates. Similar depressant effect produced by most inhalants volatile solvents, aerosols, gaseous anesthetics and nitrites. First synthesized in 1832, not used clinically until 1870. Rapidly metabolized to tri-chloroethanol, which is the active hypnotic agent. When taken orally it has a short onset of action (30 mins) 1-2 grams will induce sleep in less than an hour. Dr. benjamin richardson introduced it to great britain.