A syringe filled with Sodium Pentathol
Sodium Pentathol (generic name, thiopental sodium (C11H17N2O2SNa)) was a compound which was used as a type of "truth serum" on Earth during the mid-20th century Earth.
While he was stuck in 1947 Earth, the United States of America's Army Air Forces used Sodium Pentathol on Quark in an attempt to gain information about an anticipated attack from Mars. However, several injections of the drug did not produce results, although Quark's loud, high-pitched screams for mercy inspired Captain Wainwright to try physical threats instead. (DS9: "Little Green Men")