You know how in those old movies, people would slip a "Mickey Finn" into a drink to knock someone unconscious? It was supposed to be chloral hydrate. An early sleep medication, chloral hydrate was used to knock people out either to help them sleep, or more nefariously, as a date-rate type substance. The Mickey Finn or "knockout drops" ended up being a mixture of chloral hydrate and alcohol, which are both depressants.
Chloral hydrate is a sedative and hypnotic drug. The scientific name is trichloroacetaldehyde monohydrate, 2,2,2-trichloro-1,1-ethanediol, and is has been sold under the trade names Aquachloral, Novo-Chlorhydrate, Somnos, and Noctec. This medicine has been around for over a century and a half, having first been synthesized in 1832. Indeed, it's about the oldest synthetic drug.
In the first half of the 20th Century, chloral hydrate was used to treat insomnia and as a sedative before minor surgery. As a sleep aid it has been largely displaced by the development of z-drugs and newer hypnotics. As a sedative, it has been displaced by benzodiazepines. Doctors rarely prescribe it these days, although in rare cases it ends up being a second-line sleep agent for elderly patients. Under a doctor’s supervision it is sometimes used for pediatric echocardiography. It is also used as in veterinary medicine as a general anesthetic.
Chloral hydrate is a liquid and as a drug it is given as a liquid, either openly or inside a gelatin capsule. It is recommended that patients who get it as a liquid mix it with water or juice before swallowing. It is also recommended that food be eaten at the same time to reduce stomach inflammation. Suppositories of chloral hydrate are also available
It generally induces sleep in about an hour in therapeutic dosages. It breaks down rapidly in the body as the liver metabolizes it. The short half-life in the body is one reason it is not the best insomnia drug. Side effects include upsets to the digestive system. High doses depress respiration and blood pressure. Overdoses are possible, which is another reason it is not used much. It may also cause liver damage. Chronic use can cause dependency, which is another reason it is no longer used.
There is also some concern about chloral hydrate in drinking water, having been produced by side reactions in the chlorinated disinfection process. The concentrations are very low, and water companies monitor for this and other side products.
Chloral hydrate is a schedule IV controlled substance in the United States. It is illegal to have without a prescription.