Pop culture lies to us. Examples: IQ tests aren't that accurate a measure of pure intelligence. Polygraphs are unreliable. And truth serum is guaranteed to set a patent to babbling, but there's a good chance they won't actually be speaking the truth. io9 ran a story on Thursday about the history of sodium pentothal, aka truth serum, chronicling its invention in the early 1900s to its latter-day discreditation.
Sodium pentothal's early uses are really interesting: at one point, a doctor hoped to use some sort of truth serum to exonerate prisoners who were in jail for crimes they didn't commit. When sodium pentothal was invented in the 1930s, it was used to treat World War II soldiers recovering from shell shock. It served as a light painkiller and relaxed patients without completely knocking them out, facilitating therapy.
Of course, before long sodium pentothal moved from helping patients to convicting accused criminals. Spies and police organizations used the drug to secure confessions and information. Said information just turned out to be untrue, as often as not: sodium pentothal makes tends to make people tell their questioners whatever they want to hear. Not so good for accuracy.
The whole history of the drug is interesting, mostly because it came from such innocent origins and eventually became a pop culture icon for spy flicks. At least some outlandish spy technology from the Cold War really did exist. We always knew some of that stuff from James Bond was totally realistic.