Table 2.

Prevalence and odds of lifetime nonsuicidal self-injury (NSSI) among lifetime and early cannabis users (<17 years old) compared with their co-twin who never used cannabis or did not use cannabis early

	Lifetime prevalence of NSSI
Variable	Use/early use, n (%)	Never/late use, n (%)	Unadjusted conditional OR [95% CI]	Adjusted conditional OR [95% CI]	Significant covariates
MZ pairs discordant for cannabis use (n = 414)	14 (3.38%)	13 (3.14%)	1.08 [0.49, 2.37]	–
MZ pairs discordant for early cannabis use (n = 180)	22 (12.22%)	11 (6.11%)	3.20* [1.17, 8.73]	3.51a,* [1.19, 10.33]	Regular smoking

Notes: OR = odds ratio; CI = confidence interval; MZ = monozygotic; DZ = dizygotic.

^aAdjusted model included MZ and DZ twins (n = 379 pairs) and a zygosity interaction term to test for differences in the association between early cannabis use and NSSI in MZ and DZ twins. Covariates included childhood sexual abuse, regular smoking, illicit drug use, depressed mood, and conduct disorder.

^*p < .05.