^ Nadulski T, Pragst F, Weinberg G, Roser P, Schnelle M, Fronk EM, Stadelmann AM (December 2005). "Randomized, double-blind, placebo-controlled study about the effects of cannabidiol (CBD) on the pharmacokinetics of Delta9-tetrahydrocannabinol (THC) after oral application of THC verses standardized cannabis extract". Ther Drug Monit. 27 (6): 799–810. PMID 16306858.
Carbon dioxide is passed through the plant material at a very specific temperature and pressure. Carbon dioxide, which is normally a gas at (or above) room temperature, can be pressurized until it becomes so dense that it takes on some of the properties of a liquid while still maintaining the fluid dynamics of a gas. In this state, CO2 is known as a supercritical fluid.