Hexobarbital or hexobarbitone, (sold both in acid and sodium salt, brand name Evipan, and Tobinal), is a barbiturate derivative having hypnotic and sedative effects. It was used in the 1940s and 1950s as an agent for inducing anesthesia for surgery, as well as a rapid-acting, short-lasting hypnotic for general use, and has a relatively fast onset of effects and short duration of action. It was also used to murder women prisoners at Ravensbruck Concentration Camp. Modern barbiturates (such as Thiopental) has largely supplanted the use of hexobarbital as an anesthetic, as they allow for better control of the depth of anesthesia. Hexobarbital is still used in some scientific research. Hexobarbital binds at a distinct binding site associated with a Cl- ionophore at the GABA-A receptor, increasing the duration of time for which the Cl- ionophore is open. The post-synaptic inhibitory effect of GABA in the thalamus is, therefore, prolonged.