A new Australian study has found that insomnia patients who take medicinal cannabis containing THC show little to no impairment the following day, results that could carry significant weight in ongoing discussions about drug-driving reform.
The research team, which included representatives from the Woolcock Institute of Medical Research and the Lambert Initiative for Cannabinoid Therapeutics, recruited 20 adults diagnosed with insomnia to assess whether an evening dose of a typical medicinal cannabis oil produced any measurable impairment the next day compared to a placebo.
The participants, classified as 'infrequent' cannabis users, each received a single oral dose of 10mg THC combined with 200mg of CBD. Cognitive testing was carried out within the first two hours after waking — between nine and eleven hours following administration — with assessments targeting attention, working memory, and visuospatial function, among other measures.
Driving ability was evaluated ten hours after treatment using a simulator fitted with standard vehicle controls and a custom 30-minute scenario that had previously shown sensitivity to the acute effects of THC in healthy volunteers.
The study also tracked subjective experiences, with participants rating how 'stoned', 'sedated', 'alert', 'anxious', and 'sleepy' they felt at baseline, then at 30 minutes and again at 10 hours post-treatment.
Assessments concluded at the 10-hour mark because subjective effects were not expected to persist beyond that point following a single oral THC dose.
The researchers reported "a lack of notable 'next-day' impairment… consistent with prior work showing that the impairing effects of oral THC on cognition and driving performance typically resolve within around eight hours".
Across nearly all cognitive tests covering attention, working memory, and information processing speed, no 'next-day' effects from THC/CBD were detected.
"Overall, we found little evidence to suggest that a single dose of 10mg oral THC, in conjunction with CBD, impairs 'next-day' function in adults with insomnia who infrequently use cannabis," the researchers concluded.
"Larger studies in patient populations are required to determine the effects of repeated dosing with THC (with or without CBD), and at higher doses of THC, on 'next-day' function."
