Truth serum, also known as sodium thiopental or sodium pentothal, is a drug used to obtain information during an investigation from subjects who are unwilling to answer or somehow unable to remember the facts first-hand. There are several drugs that can be used as truth serum, including sodium thiopental (an anesthetic), grain alcohol (ethanol), scopolamine (a highly toxic depressant) and barbiturates. The same drugs have many other applications: they are used in psychiatry to treat phobias, as a general anesthesia, and even to produce medically-induced comas.

The truth serum has often been portrayed in fiction and films as a magical solution. Even the character Barty Crouch in the Harry Potter books is subjected to the use of truth serum and ends up confessing to a list of offenses. Many films, especially those that came out a couple of decades ago, when the use of the truth serum was at its peak of popularity, portrayed the serum as 100 percent effective. TV series 24, docudrama Shell Shock, and many others have used the truth serum as a plot device.

In real life, however, the use of the truth serum is highly controversial. While the serum does make a person more likely to tell the truth, it also makes them more likely to get confused. As the person becomes more and more talkative, the lines between fact and fantasy begin to blur. Experts believe that up to 50 percent of what a person says while under the influence of the truth serum is either an embellished version of the truth or a complete invention. The truth serum produces in people an effect similar to alcohol intoxication, lowering inhibitions, and making people chattier and more prone to answering questions.

Military intelligence in both the US and Russia are testing other drugs as a potential replacement for the ones currently in use. Both countries still use the truth serum in controversial cases where other methods have failed to provide an answer, including high-profile military cases, and circumstances involving national security matters.