In conclusion, after controlling for genetic and environmental confounds that might contribute to observed associations, there remained evidence consistent with non-genetic (and potentially causal) associations between some substance use/dependence measures (early alcohol use, alcohol dependence, daily nicotine use) and educational attainment, but no support for a causal relationship between other substance measures (nicotine dependence, cannabis use/dependence, any illicit drug dependence) and educational attainment. These findings lend credence to ongoing public health efforts to reduce adolescent smoking and drinking, which in turn may have beneficial effects on school dropout and lifelong educational attainment. However, the possibility that the association for alcohol and daily nicotine use is due to an unmeasured third variable (e.g., cognitive ability) needs further examination and replication in additional samples.
