Cannabis use could affect emotion processing
A first-of-its-kind review of the recent literature suggests that cannabis use could affect emotion processing, which can lead to difficulties with social relationships and possibly exacerbate the use of cannabis. The authors note, however, that more study is necessary to be certain of the findings.
A first-of-its-kind review of the recent literature suggests that cannabis use could affect emotion processing, which can lead to difficulties with social relationships and possibly exacerbate the use of cannabis. The authors note, however, that more study is necessary to be certain of the findings.
Impairments in emotion processing have already been reported in studies of individuals with alcohol and substance use disorders. Compared to control subjects, these people tended to have greater deficits in identifying emotions in facial recognition tests, were less accurate in recognizing sadness and disgust, and required greater emotional intensity to recognize fear and anger.
Recent studies in humans and rats suggest cannabis use can produce similar effects, according to a review of the recent literature on the subject by Alyssa MacKenzie and Anita Cservenka of Oregon State University. The review was published online Oct. 28, 2021, in the journal Experimental and Clinical Psychopharmacology.
Some study results
The authors compared studies of both chronic and acute cannabis users and examined the results of testing by a variety of methods including behavioral, physiological, EEG and MRI studies.
One behavioral study (Bayrakçi et al., 2015) found that deficits in the ability to detect negative facial emotions were still present after an average of 3.2 months abstinence from cannabis use. This could indicate that cannabis use induces long-lasting effects on facial emotion recognition. However, an alternative explanation could be that the emotion processing deficits precede the onset of frequent cannabis use, the authors note.
Another study (Somaini et al., 2012) compared responses to a self-assessment test and results from blood hormone level testing of 14 cannabis users, 14 abstinent cannabis users and 14 “healthy” controls. Results from the self-assessment test “indicated that active cannabis users displayed higher pleasantness ratings to unpleasant images and lower levels of arousal, compared to abstinent cannabis users and controls,” the authors note.
The same 2012 study found hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis in cannabis users as compared to non-users. The HPA axis is one of four major systems by which the hypothalamus and pituitary gland affect neurological and endocrine functioning. The authors interpret this data as supporting the behavioral effect found in the self-assessment tests.
Cannabis use and hostility––mixed results
Studies differed as to whether cannabis use increased or decreased feelings of hostility in users.
An early study (Salzman et al., 1976) showed that after smoking a 2.2% THC cigarette, the acutely intoxicated subjects experienced less hostility after social interaction than a control group not exposed to cannabis. The subjects participated in a group task of developing a consensus story for a picture. The task was designed so as to induce frustration by telling participants that their story was inadequate and had to be revised.
The authors of the literature review note, however, that this early study did not examine the subjects’ perceptions of hostility in others. Thus it is not possible to draw conclusions as to emotion processing.
More recent studies designed to measure effects of cannabis use on emotion processing found opposite results. In a 2015 study by Ansell et al., 43 recreational cannabis users reported “feelings of greater hostility and perceived others’ behavior as more hostile on days that they reported cannabis use.” Similar results were found in a 2016 study by Trull et al.
The authors note, however, two caveats concerning the more recent findings. One, that they were not collected in a laboratory or group setting, like Salzman et al., 1976, and two, the more recent sample of cannabis users had co-occurring depressive or borderline personality diagnoses.
Further, a more recent study of regular cannabis users who used a daily diary to self-report emotions found that cannabis use reduced morning levels of hostility (Testa et al., 2019).
The Oregon State study authors also examined numerous studies of effects of cannabis use as measured by electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) partly to distinguish acute from chronic effects.
Electroencephalography studies “have produced mixed findings,” they report. Results of functional MRI studies of amygdalar brain activity are also mixed, although “several studies indicate that cannabis use is linked with decreased brain response in the frontal lobe while viewing emotional stimuli.”
They also looked at studies that examined possible differences in the effect of the tetrahydrocannabinol (THC) and cannabidiol (CBD) components of cannabis, and on acute vs. chronic effects.
Public health significance and further research
The authors also note the possible public health significance of their results.
“Studies synthesized in this review article suggest that cannabis users may have impairments in emotion processing at the behavioral, physiological, and neural level," they wrote. "Understanding these difficulties could aid prevention, intervention, and treatment efforts aimed at promoting healthy socio-emotional functioning in cannabis users.”
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A. MacKenzie & A. Cservenka. Cannabis and emotion processing: A review of behavioral, physiological, and neural responses. Experimental and Clinical Psychopharmacology (2021).
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