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Methaqualone, also called Quinazolinone, is a sedative hypnotic drug.

Methaqualone tablets and capsules.

It is similar in effect to barbiturates, a general CNS depressant. It was used in the 1960s and 1970s as an anxiolytic, for the treatment of insomnia and as a sedative.

Usual effects include relaxation, euphoria and drowsiness, it also reduces heart rate and respiration. Larger doses can bring about depression, muscular miscoordination and slurred speech. An overdose can cause delirium, convulsions, hypertonia, hyperreflexia, vomiting, renal insufficiency, coma, and possibly death through cardiac or respiratory arrest. It resembles barbiturate poisoning but with increased motor difficulties and a lower incidence of cardiac or respiratory depression. Toxicity is treated with diazepam and sometimes an anticonvulsant.

Methaqualone was discovered by the Indian researcher M. L. Gujiral in 1955 during a antimalarial research program. It was marketed as a sleeping pill from the 1960s under a number of tradenames including Renoval, Melsed and in combination with an antihistamine as Mandrax. From 1965 it was sold on the US market as Quaalude, Sopor and Parest, by 1972 it was the sixth most popular sedative in the US. The name Quaalude was apparently derived from the phrase 'quiet interlude' with an added 'aa' by the manufacturers. It was hoped that it was a 'safer' drug than barbiturates to use for sedation; however, it was found to have similar problems of tolerance and dependence.

Quaaludes became increasingly popular as a recreational drug during the 1960s. The drug was more tightly regulated in Britain under the 1971 Misuse of Drugs Act and in the US from 1973. With its addictive nature clear, it was withdrawn from many developed markets in the 1980s, being made a Schedule I drug in the US in 1984.

Chemical names include 2-Methyl-3-o-tolyl-4(3H)-quinazolinone, 3,4-dihydro-2-methyl-4-oxo-3-o-tolylquinazoline, and 2-methyl-3-(2-methylphenyl)-4-(3H)-quinazolinone. Empirically it is C16H14N2O.