Hexahydrocannabinol: pharmacokinetics, systemic toxicity, and acute behavioral effects in Wistar rats

Abstract

Background: Hexahydrocannabinol (HHC) is a new psychoactive substance known for its mind-altering effects and temporary legal status. It is widely used in parts of the Europe and United Kingdom as a legal alternative to ∆9-tetrahydrocannabinol, yet little research has explored its effects and safety. This study examined how HHC is processed in the body, its toxicity, and its impact on behavior in male Wistar rats.

Methods: A 1:1 mixture of (9R)-HHC and (9S)-HHC was administered via intragastric gavage at doses of 1, 5, and 10 mg/kg. Behavioral effects were assessed using the open field test and the prepulse inhibition of acoustic startle response.

Results: Two hours after the highest dose (10 mg/kg), peak concentrations of HHC were detected in blood and brain tissue. The Organization for Economic Co-operation and Development 423 toxicity test classified HHC as a Category 4 substance, estimating a lethal dose of 1000 mg/kg. Compared to controls (administered by sunflower oil), 10 mg/kg HHC reduced movement, increased anxiety, and impaired sensory processing.

Conclusions: Overall, HHC crosses the blood-brain barrier, exhibits mild toxicity, and induces behavioral effects similar to tetrahydrocannabinol. Its dose-dependent anxiogenic properties and impact on information processing highlight the importance of the appropriate dosing in any potential therapeutic use.

Keywords: acute toxicity; behavior; hexahydrocannabinol; pharmacokinetics; rat.

Figure 1

Monte Carlo simulation of the theoretical distribution of R-hexahydrocannabinol (R-HHC) and S-hexahydrocannabinol (S-HHC) serum concentration - time profiles in rats after oral administration of 10 mg/kg of HHC racemic mixture. The solid line represents the median, and the shaded bands represent the 90% prediction interval percentiles of the simulated concentration distribution.

Figure 2

Mean ± SD blood/serum concentration ratio–time profiles of R-hexahydrocannabinol (R-HHC) and S-hexahydrocannabinol (S-HHC) in rats after oral administration of 10 mg/kg of HHC racemic mixture. ^*P = .0444; ^**P = .0019 (paired t-test).

Figure 3

Results of the Open field test (OFT) and Prepulse inhibition of acoustic startle response (PPI ASR) are presented in the panel. (A) OFT: trajectory length in 5-min intervals, mean ± SEM for each dosage at 5-minute intervals are presented, Linear Mixed Model (LMM); (B) OFT: thigmotaxis, individual values are shown; (C) OFT: an example of characteristic trajectories for each treatment; (D) OFT: time in the centre, individual values are shown; (E) PPI ASR: Acoustic startle response (ASR), individual values are shown; (F) PPI ASR: Prepulse Inhibition (PPI), individual values are shown. (B) – (F) ANOVA followed by Dunnett's post hoc; significant differences from the control group values are marked by ^*P < .05, ^**P < .01, ^***P < .001.