Glossary
Delta-9 THC
Updated:
Delta-9 tetrahydrocannabinol is the main intoxicating cannabinoid in cannabis. Federal law uses it to separate hemp from marijuana: hemp holds not more than 0.3 percent delta-9 THC on a dry weight basis. From December 11, 2026, the test shifts to total THC, which also counts THCa.
Delta-9 tetrahydrocannabinol is the compound mainly responsible for the mental effects of cannabis (NCCIH). It acts as a partial agonist at CB1 receptors, which are the most abundant cannabinoid receptors in the central nervous system (Lu and Mackie 2016).
The plant makes delta-9 THC as THCa, its acid form, and heat converts THCa to delta-9 THC. That is why raw flower tests high in THCa and low in delta-9 THC until it is smoked, vaped or cooked.
Federal law draws the hemp line at delta-9 THC: not more than 0.3 percent on a dry weight basis (7 U.S.C. 1639o). Section 781 of Public Law 119-37 rewrote that definition to use total tetrahydrocannabinols, including the acid, and to cap final products at 0.4 mg total THC per container. Public Law 119-103 limited those changes to synthetic cannabinoids until December 11, 2026, after which the full definition applies (P.L. 119-103).
Full-spectrum hemp products contain small amounts of delta-9 THC. Broad-spectrum and isolate products are processed to remove it to non-detect levels.
Sources
- Cannabis (Marijuana) and Cannabinoids: What You Need To Know NIH National Center for Complementary and Integrative Health (accessed 2026-10-13)
- 7 U.S.C. 1639o, Definitions (hemp) Cornell Legal Information Institute (accessed 2026-10-13)
- Public Law 119-103, Continuing Appropriations and Extensions Act, 2027, section 2019 GovInfo (accessed 2026-10-13)
- An Introduction to the Endogenous Cannabinoid System (Biol Psychiatry, 2016) PubMed (accessed 2026-10-13)