CBD, THC and Facial Emotion Recognition: Better Test Scores Without Feeling Less Stoned

Adding CBD to THC improved a specific facial-emotion recognition comparison without making participants feel less stoned. The controlled study illustrates why a change in one cognitive outcome should not be described as a general reversal of THC intoxication.

Four conditions in the same participants

Hindocha and colleagues recruited 48 cannabis users for a randomized, double-blind crossover study. Participants received placebo, THC, CBD and the combination on separate days. The preparations loaded into the vaporizer contained 8 mg THC, 16 mg CBD, or both; the paper distinguishes the loaded quantities from the smaller amounts expected to be inhaled.

The task presented faces showing different emotions at varying intensities. Recognizing a weakly expressed emotion is a different demand from recognizing an unmistakable expression. The investigators also collected subjective ratings, including how stoned participants felt.

The effects depended on expression intensity

THC reduced recognition accuracy relative to placebo at 40% emotional intensity. CBD alone improved accuracy at 60% intensity. An exploratory comparison found better performance with the combination than THC alone at 40%, and the combination did not show the same impairment relative to placebo there.

The combination nevertheless produced subjective feelings of being stoned comparable to THC alone. The results therefore separate performance on this particular task from the intensity of the reported drug experience. They do not show that CBD made all cognitive functions normal.

What the study does not establish

One participant’s facial-task data were excluded as an outlier. Recruitment by cannabis-use frequency and schizotypy produced small subgroups, and some participants’ characteristics changed between initial recruitment and testing. The researchers also lacked urine screening to verify between-session abstinence.

The task involved brief, standardized pictures, not a witness interpreting a complex live event or a driver responding to traffic. Neither the selective benefit nor the null findings establish a universal protective CBD-to-THC ratio.

The practical question is which outcome a claimed “protective” effect actually concerns. Our discussion of selective spatial-working-memory findings gives another example of why cannabis-related cognitive effects should be described at the level of the tested function.

Primary research

Acute effects of delta-9-tetrahydrocannabinol, cannabidiol and their combination on facial emotion recognition: A randomised, double-blind, placebo-controlled study in cannabis users. DOI: 10.1016/j.euroneuro.2014.11.014.