0.3% threshold

The 0.3% threshold is the delta-9 THC concentration ceiling that distinguishes hemp from marijuana under federal law. Established by the 2018 Farm Bill at 7 U.S.C. § 1639o, cannabis plant material testing at or below 0.3% delta-9 THC on a dry-weight basis is classified as "hemp" and exempt from the CSA; material exceeding 0.3% is "marihuana" and a Schedule I controlled substance. The 0.3% figure originated in a 1976 taxonomic paper by Ernest Small and Arthur Cronquist as a botanical marker, not a pharmacological one, and has been criticized as arbitrary. The threshold applies at harvest; USDA rules require pre-harvest testing within a 30-day window using post-decarboxylation total THC measurement (delta-9 + THCA × 0.877). P.L. 119-37 (Nov. 12, 2025) retained the 0.3% plant-material threshold but redefined it in terms of total THC (delta-9 plus THCA and similar cannabinoids) and added a separate 0.4 mg total THC per container cap for finished consumer products, effective November 12, 2026. *→ See also: Hemp, 2018 Farm Bill, Marijuana