Changes in delta-9-tetrahydrocannabinol (THC) and cannabidiol (CBD) concentrations in cannabis over time: systematic review and meta-analysis Posted on December 6, 2021February 3, 2022 By Becky Carter Tom P. Freeman, Sam Craft, et al Addiction; 116(5); 2021 Download the article Cannabis and Cannabinoids, Seized Drugs/Controlled Substances, Toxicology