Sirius IX was the inhabited ninth planet of the Sirius system. This Alpha Quadrant planet was located approximately eight light years from Earth. This was the homeworld of the Sirius IX natives, a humanoid species with an unique biochemistry.
In the mid-23rd century, Harry Mudd sold a love potion to a thousand people on Sirius IX. When they became ill, Mudd quickly left the planet. (TAS: "Mudd's Passion")