Veritaserum does exist, or at least, a variation of it does.

The military uses "truth drugs" to extract information from prisoners of war. Acording to The EXTREME Survival Guide by Rory Storm (in the "Surviving... the Enemy" section),

An injection of a "truth drug" (a chemical compound which overcomes the subject's conscious resistance) may be used to make a prisoner divulge secret information. It is almost impossible to withstand the disabling effects of this drug. However, it is not widely available and more brutal ways of extracting information are often employed. (p. 80)

Given what the truth drug does, compare it to Veritaserum:

Dumbledore forced the man's mouth open and poured three drops inside it. Then he pointed his wand at the man's chest and said, "Enervate."
   Crouch's son opened his eyes. His face was slack, his gaze unfocused.
... Crouch took a deep, shuddering breath, then began to speak in a flat, expressionless voice.
(GoF, chapter 35)

Bibliography
Storm, Rory. EXTREME Survival Guide, The. Boston, Massachusetts: Element Children's Books, 1999. .