Cannabis Involvement and Nonsuicidal Self-Injury: A Discordant Twin Approach

Abstract

ABSTRACT. Objective: Cannabis use, particularly at an early age, has been linked to suicidal thoughts and behavior, but minimal work has examined the association between cannabis use and lifetime nonsuicidal self-injury (NSSI). The current study aims to characterize the overlap between lifetime and early cannabis use and NSSI and to examine genetic and environmental mechanisms of this association. Method: Adult male and female twins from the Australian Twin Registry (N = 9,583) were used to examine the odds of NSSI associated with lifetime cannabis use and early cannabis use (i.e., <17 years of age). These associations were also examined within monozygotic (MZ) twins discordant for cannabis use and MZ twins discordant for early cannabis use. Analyses were replicated in an independent sample of female twins (n = 3,787) accounting for the age at onset of cannabis use and NSSI. Conclusions:Results suggest that NSSI is associated with cannabis involvement via differing mechanisms. For lifetime cannabis use, the lack of association in discordant pairs suggests the role of shared genes and family environment. However, in addition to such shared familial influences, person-specific and putatively causal factors contribute to the relationship between early cannabis use and NSSI. Therefore, delaying the onset of cannabis use may reduce exposure to influences that exacerbate vulnerabilities to NSSI. (J. Stud. Alcohol Drugs, 77, 873-880, 2016)

Cannabis use, depression and self‐harm: phenotypic and genetic relationships

“…Significant genetic correlations between cannabis use, depression and self‐harm were also in line with some , but not all previous findings in family studies. The genetic correlation between cannabis use and depression estimated here was higher than those previously published using the same methodology , probably reflecting the increased power of more recent depression GWA analyses.…”

“…In addition to depression, cannabis use has also been associated with increased rates of self‐harm, both for non‐suicidal and suicidal behaviours. This phenotypic association may be stronger than that observed between cannabis and depression, but while some studies have reported evidence of a shared genetic aetiology , others found that genetic factors were less important . Therefore, additional work exploring how cannabis use related to self‐harm is also needed.…”

Cannabis use, depression and self-harm: phenotypic and genetic relationships

“…Despite evidence of significant interactions between cannabis phenotypes with sex and alcohol use, stratified analyses suggested that this pattern of association was consistent across sex, smoking or alcohol consumption. Significant genetic correlations between cannabis use, depression and self-harm were also in line with some [15,23,24], but not all [16] previous findings in family studies. The genetic correlation between cannabis use and depression estimated here was higher than those previously published using the same methodology [13], probably reflecting the increased power of more recent depression GWA analyses.…”

“…In addition to depression, cannabis use has also been associated with increased rates of self-harm, both for non-suicidal [19][20][21] and suicidal [16,22,23] behaviours. This phenotypic association may be stronger than that observed between cannabis and depression, but while some studies have reported evidence of a shared genetic aetiology [23,24], others found that genetic factors were less important [16,25]. Therefore, additional work exploring how cannabis use related to self-harm is also needed.…”

The Impact of Cannabis Use Disorder on Suicidal and Nonsuicidal Self‐Injury in Iraq/Afghanistan‐Era Veterans with and without Mental Health Disorders

“…The disinhibition theory argues that cannabis intoxication leads to disinhibition, which, in turn, directly increases users’ risk for self‐injury (Delforterie et al., ). It is also possible that variables not considered in the present analyses (e.g., attention‐deficit/hyperactivity disorder, childhood sexual abuse) might increase risk for both conditions (Few et al., ). Finally, as noted by Few and colleagues (), repeated exposure to 9‐tetrahydrocannabinol (THC) and endocannabinoids through chronic cannabis use could also potentially modulate users’ pain perception, thereby increasing their risk for self‐injury, particularly nonsuicidal self‐injury.…”