ArticlePsychological medicine2026
The causal impact of older siblings' academic achievement on younger siblings' risk for drug use disorder: instrumental variable and propensity score analyses.
Article in Psychological medicine, 2026. The graph could read no effect estimate from its abstract, so it casts no vote on the map. Not yet cited in PubMed.
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Abstract
backgroundDrug use disorder (DUD) clusters in families due partly to shared environment, including sibling influences. Low academic achievement (AA) in adolescence increases DUD risk. This study examined whether low AA in an older sibling causally increases DUD risk in younger siblings.
methodsWe studied all Swedish full sibling pairs (
resultsOlder sibling AA significantly predicted younger sibling DUD risk across models. Beta coefficients (±95% CI) were 2.04 (1.97-2.12) in raw analysis, 1.88 (0.74-3.02) in IV, and 1.26 (1.17-1.34) in PS models. Together with the strong first-stage association, the IV estimates remain positive under small departures from the ideal identifying assumptions. Effect sizes declined with increasing sibling age differences (
conclusionsFindings from two causal inference approaches support a largely causal link between low AA in an older sibling and increased DUD risk in younger siblings. Stronger effects in close-aged and male-male pairs further support this conclusion. Interventions to improve AA in older siblings may yield indirect preventive benefits for younger siblings.
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