TABLE 1.

Results of the Mendelian randomization analyses using summary‐level data from liability to ADHD to substance use risk including IVW estimates and four sensitivity analyses: weighted median, weighted mode, MR‐Egger, and GSMR

Exposure	Outcome	n SNPs a	IVW				WeightedMedian				Weighted Mode				MR‐Egger				n SNPs a	GSMR
			β	OR	95% CI	P	β	OR	95% CI	P	β	OR	95% CI	P	β	OR	95% CI	P		β	OR	95% CI	P
ADHD	Smoking initiation	10	.07		0.03 to 0.11	1.7e−05	.05		0.03 to 0.07	4.2e−05	.05		0.03 to 0.07	.010	.01		−0.13 to 0.15	.937	8	n.a.		n.a.	n.a.
ADHD	Cigarettes/d	10	.04		0.02 to 0.06	.006	.05		0.01 to 0.09	.004	.05		−0.01 to 0.11	.089	−.11		−0.25 to 0.03	.127	8	n.a.		n.a.	n.a.
ADHD	Smoking cessation	11	−.03		−0.05 to −0.01	.005	−.03		−0.05 to −0.01	.026	−.03		−0.07 to 0.01	.215	.06		−0.04 to 0.16	.255	9	n.a.		n.a.	n.a.
ADHD	Lifetime smoking	10	.10		0.06 to 0.14	8.8e−08	.09		0.05 to 0.13	1.6e−09	.10		0.06 to 0.14	.003	n.a.		n.a.	n.a.	9	n.a.		n.a.	n.a.
ADHD	Alcohol drinks/wk	10	−.01		−0.05 to 0.03	.741	.02		0.00 to 0.04	.150	.02		0.00 to 0.04	.153	.08		0.06 to 0.10	.468	7	n.a.		n.a.	n.a.
ADHD	Alcohol problems	10	.01		−0.01 to 0.03	.234	.00		−0.02 to 0.02	.729	.00		−0.02 to 0.02	.815	n.a.		n.a.	n.a.	8	n.a.		n.a.	n.a.
ADHD	Alcohol dependence	12	.07	1.07	1.01 to 1.14	.030	.06	1.06	0.96 to 1.17	.230	.07	1.07	0.93 to 1.23	.378	−.16	0.85	0.60 to 1.21	.407	10	.06	1.06	0.98 to 1.15	.094
ADHD	Cannabis initiation	10	.12	1.13	1.02 to 1.25	.010	.17	1.19	1.05 to 1.34	.001	.19	1.21	0.97 to1.52	.107	n.a.	n.a.	n.a.	n.a.	10	.11	1.12	1.03 to 1.21	.004
ADHD	Cups of coffee/d	9	.03		−0.03 to 0.09	.322	.04		−0.04 to 0.12	.331	.05		−0.09 to 0.19	.458	n.a.		n.a.	n.a.	9	n.a.		n.a.	n.a.

Note. The dichotomous variables smoking initiation and smoking cessation were rescaled in the original GWAS such that its unit is a standard deviation increase in prevalence. ¹⁷ The beta coefficients in this table represent the change in outcome per 2.72‐fold increase in the prevalence of ADHD diagnosis (due to the log odds nature of the ADHD GWAS data). For MR‐Egger, when I ² was 0.6‐0.9, a SIMEX correction was applied, while estimates were not reported at all when I ² was <0.6.

Abbreviations: GSMR, generalized summary data–based Mendelian randomization; GWAS, genome‐wide association studies; n SNPs, number of SNPs included in the genetic instrument; n.a., the number of SNPs available for the analysis was too low or, in the case of MR‐Egger, I ² was <0.6; SE, standard error of the beta; SIMEX, simulation extrapolation.

^aNumber of SNPs left after the HEIDI filtering step which is part of GSMR.