Rick Simpson Oil (RSO) is a highly potent, full-spectrum cannabis extract known for its thick, dark, and sticky consistency, containing high levels of tetrahydrocannabinol (THC). RSO is produced by using the whole cannabis plant—including leaves, trim, and flower—to create a full spectrum extract, retaining a wide range of cannabinoids, terpenes, and fats. It was developed by Canadian medical marijuana activist Rick Simpson to treat his own skin cancer.