Written by Chrystal Moulton, Staff Writer. Compared to delta-9-tetrahydrocannabinol (THC) inhaled alone or in combination with cannabidiol (CBD), inhaled CBD demonstrated a reduction in psychotic-like symptoms in light users of cannabis.
In the current study10, researchers tested the effect of inhaled CBD alone and in combination with THC using a randomized, double-blind crossover design. The 48 selected study participants were cannabis users who had previously participated in another large scale trial. They were evenly divided into two groups: 24 light users and 24 heavy users of cannabis. Participants were matched across both groups of users based on age, schizotypal personality trait, and verbal intelligence. In all, they were four groups of participants and 4 sessions of testing (see table 1 below). All subjects received one of the four treatments below followed by cognitive measures to determine the effects of treatment on memory and cognitive function. One-week washout period was given between treatment sessions. Researchers predicted that individuals with high schizotypal personality and light users of cannabis would show sensitivity to the psychoactive effects of THC, CBD, and the combination of THC and CBD. They also predicted a protective effect of CBD when administered together with THC.
Table. 1 Overview of participant classification and experimental treatments
| Participant categories | Treatment sessions | Drug preparation (for inhalation) |
|---|---|---|
| light user-low schizotypy | THC (8mg) | dissolved in EtOH |
| light user-high schizotypy | CBD (16mg) | dissolved in EtOH |
| heavy user-low schizotypy | THC (8mg)+CBD (16mg)* | dissolved in EtOH |
| heavy user-high schizotypy | placebo | Ethanol |
*2:1 ratio reflects upper limit commonly found in high CBD/low THC preparations
Results showed a strong positive correlation between psychotic-like symptoms and THC (p=0.014) as well as THC+CBD combination (p=0.022) compared to placebo. No overall correlation was found for CBD alone. THC and THC+CBD were associated with increased scores in perceptual distortion (THC p=0.006; THC+CBD p=0.005) and cognitive disorganization (THC p=0.008; THC+CBD p=0.004). On the psychiatric rating scale, THC and THC + CBD increased scores for negative symptoms compared to placebo (p=0.025 and p=0.008, respectively). Poorer recall was also found following THC (p=0.031) and THC+CBD (p=0.024) administration relative to placebo. CBD alone was associated with reduced psychotic-like symptom scores in light users (p=0.015) but not heavy users (p=0.104). CBD alone also improved performance compared to placebo on a cognitive test measuring processing speed called the Trail Making Test (p=0.045). However, it was also found that long history of cannabis use was associated with blunted antipsychotic effects of CBD (r=0.434, p=0.034).
Ultimately, researchers found that CBD given with THC in a 2:1 ratio had no protective effects against the psychoactive symptoms associated with THC when compared to placebo and CBD alone. No cognitive impairment or psychoactive symptoms were associated with CBD administration. Furthermore, CBD administration alone was associated with a reduction in psychotic-like symptoms in light users compared to heavy. More research will be needed to determine the therapeutic potential of CBD for psychosis.
Source: Morgan CJA, Freeman TP, Hindocha C, Schafer G, Gardner C, Curran HV. Individual and combined effects of acute delta-9-tetrahydrocannabinol and cannabidiol on psychotomimetic symptoms and memory function. Transl Psychiatry. 2018;8(1):181.
© The Author(s) 2018 licensed under a Creative Commons Attribution 4.0 International License, http://creativecommons.org/licenses/by/4.0/.
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Posted January 21, 2019.
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- Morgan CJ, Freeman TP, Hindocha C, Schafer G, Gardner C, Curran HV. Individual and combined effects of acute delta-9-tetrahydrocannabinol and cannabidiol on psychotomimetic symptoms and memory function. Translational psychiatry. 2018;8(1):181.
