THC's Hidden Effects: What Happens When You Use Cannabis Before Bed?

Disordered sleep is a common reason individuals report using cannabis, yet the physiological effects of Δ9-tetrahydrocannabinol (Δ9-THC) on sleep and autonomic regulation remain incompletely understood. Early studies reported acute sleep-promoting effects of Δ9-THC, but chronic use has been associated with disrupted sleep and possible cardiovascular risk. This feasibility and mechanistic pilot study examined the influence of acute Δ9-THC administration on sleep and cardiac parasympathetic activity in adults with and without regular cannabis use. Nine individuals with regular cannabis use (> 3× per week) and nine individuals with minimal cannabis exposure (no use within the previous year and < 10 lifetime exposures) underwent 2 weeks of actigraphy-verified sleep stabilisation before a three-night, single-blind laboratory protocol including an acclimatisation night, a placebo night, and a 10 mg oral Δ9-THC dosing night. During at-home monitoring, individuals who regularly used cannabis (permitted ad libitum cannabis use) had shorter total sleep time and greater sleep disruption than the no cannabis use group (p < 0.05). In laboratory polysomnography revealed that Δ9-THC increased sleep latency, slow wave sleep (p < 0.05), EEG spectral power across frequency bands (p < 0.05), and attenuated delta power dissipation in the first half of the night (DrugxSleephour, p < 0.05). Δ9-THC also markedly reduced heart rate variability across time- (p < 0.01) and frequency-domain (p < 0.05) metrics. These findings demonstrate the feasibility and tolerability of controlled in-laboratory Δ9-THC administration following sleep stabilisation among adults who regularly use cannabis and those with minimal exposure, and provide preliminary mechanistic evidence that acute Δ9-THC before bedtime increases cortical activation and reduces cardiac parasympathetic activity during sleep.