Herbal teas of fiber-type hemp varieties (Cannabis sativa L.) rich in cannabidiolic acid (CBDA) and cannabidiol (CBD) and poor in Δ9-tetrahydrocannabinol acid (THCA) and Δ9-tetrahydrocannabinol (THC) are very popular today. The conditions for preparing herbal infusions are not well standardized and analysis of the lipophilic cannabinoids in infusions is difficult. Therefore, we analyzed the hemp leaf residues after tea preparation by using a response surface modelling approach to estimate the effects of variations in temperature, water volume and extraction time on the residual content of five cannabinoids (CBDA, CBD, THCA, THC, cannabinol (CBN)) in the hemp leaves after extraction. The quantity of remaining cannabinoids was mainly influenced by temperature in the first order. Volume and extraction time were only exerting minor influences under usual tea preparation processes. At elevated water temperatures CBD and THC values were even higher than in the original drug material presumably due to decarboxylation of CBDA and THCA. Rising temperatures increased extraction of CBDA and CBD, as opposed to THCA and THC. The degradation of THC to CBN was not significant at the conditions of infusion preparation. Analyzing herbal residues after tea brewing is just an approximation to the true values of valuable or unfavorable compounds in tea, overestimating the true values. However, that approach offers a good control for further improvements of herbal tea analysis and gives reliable indications for risk assessment.
