Answer: Both classes of drugs are depressants useful for a variety of psychiatric conditions like insomnia or anxiety, but benzodiazepines are generally considered the safer of the two drugs.
The earliest barbiturate drugs were tested in 1903 by the Bayer drug company as an anesthetic that could help put dogs to sleep. Chemically, these compounds were made from synthesis with urea and malonic acid. After the discovery had been made, according to urban legend, they had gone to a nearby tavern to celebrate, where others were celebrating the feast of Saint Barbara.
It was found that these barbiturate drugs had more use other than for veterinary purposes, and more commonly used barbiturates such as phenobarbital were developed soon after. These drugs were used widely, functioning as a sleep aid. However, the negative side effects of barbiturates, such as their addictive properties and depressant effects on the respiratory system, weren't characterized until the 1950s (The American Psychiatric Publishing Textbook of Substance Abuse Treatment).
Because of their effects on people, barbiturates were used in several nonmedical contexts. They have been delivered at high doses in cases of physician-assisted suicide and as a precipitating agent in the American death penalty by lethal injection (ADMINISTRATION AND COMPOUNDING
OF EUTHANASIC AGENTS).
The risks associated with barbiturate overdose led researchers to develop drugs with similar benefits without the negative harms. In 1955, the first benzodiazepine drug called chlordiazepoxide (Librium) was created by Leo Sternbach at the Hoffman LaRoche company. At first, it was unsuccessful, but with some changes to the process, they were able to develop a drug with the same sedative and muscle relaxant properties. These benzodiazepine drugs turned out to be much safer than the barbiturates used before them, even though they have a similar pharmacological site of action at the GABA receptor.
However, the benzodiazepines are not perfectly safe and still have risks associated with them. Long term use of benzodiazepines could lead to anxiety or depression. People who use benzodiazepines to help with insomnia may experience drowsiness the next morning, which has led to motor vehicle accidents. Benzodiazepines are controlled substances because they are potentially dependence causing, and making them addictive. People who misuse benzodiazepines usually use them in a poly-drug abuse pattern, taking the drug in conjunction with other psychoactive drugs.