Acute subjective effects after smoking joints containing up to 69 mg Δ9-tetrahydrocannabinol in recreational users a randomized, crossover clinical trial.
An increase in the potency of the cannabis cigarettes has been observed over the past three decades. In this study, we aimed to establish the impact of Δ9-tetrahydrocannabinol (THC) on the rating of subjective effects (intensity and duration of the effects), up to 23 % THC potency (69 mg THC) among recreational users. Recreational users (N 24) smoked cannabis cigarettes with four doses of THC (placebo 29, 49 and 69 mg of THC) on four separate test days in a randomized, double-blind, placebo-controlled, crossover study. The participants filled in three different questionnaires measuring subjective effects during the exposure up to 8 h post-smoking. The high feeling, heart rate, blood pressure and THC serum concentrations were also regularly recorded during these 8 h. THC significantly increased the high feeling, dizziness, dry-mouthed feeling, palpitations, impaired memory and concentration, and down, sedated and anxious feelings. In addition, THC significantly decreased alertness, contentment and calmness. A cubic relationship was observed between feeling the drug and wanting more. The THC-induced decrease in feeling stimulated and increase in anxiety lasted up to 8 h post-smoking. Sedation at 8 h post-smoking was increased by a factor of 5.7 with the highest THC dose, compared to the placebo. This study shows a strong effect of cannabis containing high percentages of THC on the rating of subjective effects. Regular users and forensic toxicologists should be aware that the THC-induced increase in feeling sedated continues longer with a 69 mg THC dose than with a 29 mg THC dose.