Harry Mudd's love crystals
A love potion was any type of chemical or magical element that was capable of making someone fall in love with the one who administers the potion.
The tears of Elasian females, when in contact with males, were biochemically capable of acting as a love potion, making them easy to enslave men. They worked by infecting the male who made such physical contact; Dr. Leonard McCoy formulated an antidote to that infection. (TOS: "Elaan of Troyius")
Harry Mudd had love crystals that were filled with a liquid, the actual potion, but once its main effect wore off, it had a powerful, and far longer-lasting, rebound effect. (TAS: "Mudd's Passion")
A love philtre was a magical type of love potion used by the Megans. (TAS: "The Magicks of Megas-Tu")