Ryll was a relatively weak form of spice used to create a number of medicines used throughout the galaxy. It could be combined with glitterstim to create glitteryll. Ryll kor was another type of ryll, used primarily for medical purposes.
Ryll was discovered around 4,800 BBY and mined on the planet Ryloth, although it was presumably found on other planets such as Naos III. It was also smuggled into the Corporate Sector for illegal sale to the workers. As with many substances used for illegal recreation, ryll had the potential to be very addictive and dangerous. In addition to the mining operations on Ryloth, just before the Battle of Yavin the Hutts used slaves from a false religion to produce the spice on the planet Ylesia until the Rebel Alliance involved themselves with the operations and ultimately forced the shut down of the planet's spice ring.