Legal Drug (Japanese: 合法 ドラッグ, Hepburn: Gōhō Doraggu) is a manga series by Clamp.

When Kazahaya Kudo collapsed in the snow one night and on the verge of death, he is rescued by a mysterious young man, Rikuo Himura, who takes him back to a pharmacy named the Green Drugstore.

In the second volume of Legal Drug, Kakei purchases clothes from "Piffle Princess" for Kazahaya to give to a girl from Ohto High in exchange for her uniform.

Piffle Princess also appears in other CLAMP works, including Chobits, xxxHolic, Tsubasa: Reservoir Chronicle, Kobato, and Cardcaptor Sakura.

Written by Clamp, the chapters of Legal Drug appeared as a serial in the manga magazine Mystery DX from November 2000 to May 2001.

In 2001, it resumed serialization in Shojo Teikoku from July to November; afterwards, it was transferred to Asuka, where it ran from June 2002 to September 2003.