The Venus drug was an illegal chemical compound supposedly capable of enhancing one's most attractive qualities. Considered by many to be merely a myth, the drug was said to make women more beautiful and alluring, and men more muscular and aggressive.
In 2266, the interstellar criminal Harcourt Fenton Mudd utilized the drug on three women whom he intended to provide as wives to settlers on planet Ophiucus III. En route, however, Mudd's starship was intercepted by the crew of the USS Enterprise, and subsequently destroyed in an asteroid belt. Mudd and the women were brought aboard the Enterprise, and Mudd subsequently hid the drug, due to its illegal nature. Later, on planet Rigel XII, Mudd used the drug in an attempt to make the women more appealing to three lithium miners, agreeing to provide the women as wives in exchange for the miners using their leverage over Captain Kirk to have Mudd freed. Kirk, however, was able to set up a ruse whereby one of the women, Eve McHuron, took colored gelatin in place of the drug and, upon witnessing Eve experience identical effects as that of the actual drug, and prove that the drug's power actually resided in the user's self-confidence and belief in their own attractiveness. (TOS: "Mudd's Women")