An illegal drug that temporarily makes its user strikingly more attractive, supplied by Harry Mudd to three women he was transporting as brides for lonely settlers.
The Venus drug is at the heart of the episode Mudd's Women. When the Enterprise rescues the swindler Harry Mudd and his three passengers, Eve, Ruth and Magda, the women have an almost hypnotic effect on the male crew.
The effect is chemical. Mudd is giving them pills that heighten whatever a person already has, making women appear more beautiful and men more forceful, and the result wears off within hours to leave the user plain and exhausted.
Mudd uses the women to bargain with the lithium miners of Rigel XII, whose crystals the ship badly needs. The deception is exposed when Eve refuses to continue. She then takes what she believes is the drug and becomes radiant again, although Kirk has given her a harmless substitute.