THC Content on a Dry Weight Basis: Implications for Hemp Legality

The 2018 Farm Bill defines hemp as Cannabis sativa L. with a tetrahydrocannabinol (THC) concentration not more than 0.3% on a dry weight basis where THC is implied to be total THC (THCTotal) including both acid (Δ9-THCA) and neutral (Δ9-THC) forms.

Effect of temperature and mass were studied to determine the quickest time to prepare fresh hemp suitable for grinding without affecting THCTotal. Proficiency testing program data were also analyzed to compare THCTotal contents on a dry versus wet weight basis.

Fresh hemp of 150 and 400 g were freeze-dried or heat-treated at 50°C, 60°C, and 70°C for various lengths of time up to 72 h. Ground hemp was analyzed for moisture content via AOAC 934.01 and THCTotal via liquid chromatography/mass spectrometer (LC/MS) or gas chromatography with flame ionization detection (GC/FID). A data set analyzed from a proficiency testing program included moisture and THCTotal from 20 to 67 laboratories on 12 analytical samples circulated from 2020 through 2022.

The quickest drying time of 24 h occurred at 70°C with 150 g. These conditions did not affect THCTotal content on a dry weight basis. Twelve proficiency testing program analytical samples ranged from 5.8% to 11.4% moisture and 0.144% to 0.399% THCTotal on a wet weight basis. An increase in reported THCTotal on a dry weight basis compared to a wet weight basis ranged from 0.002% to 0.027% with a significant difference occurring in only one analytical sample.

Suitable conditions for drying hemp without altering THCTotal content were 24 h at 70°C. Determining residual moisture in oven-dried ground hemp to calculate THCTotal content on a dry weight basis provides no benefit given the minimal difference between contents on dry versus wet weight bases, interlaboratory variability, and terpene volatilization.