This is a class of drug derived from barbituric acid that is often used for medical purposes as a sedative and/or hypnotic. The effects barbiturates produce are similar to alcohol, causing feelings of depression, sleepiness, impaired judgment, and reduced inhibitions. Barbiturates fall under the "depressant" drug class and can be very addictive.
One example you are probably familiar with is Pentothal, also known as truth serum. This barbiturate (and the reason people refer to it as truth serum) is because it produces a drunken-like state during which people are less inhibited and more likely to tell the truth.