Several limitations in this study should to be noted. Although we did not find differences on demographic variables, these three groups of adolescents could differ on a variable not assessed. Since analyses were not longitudinal, we cannot ascertain if changes resulted from substance use or were preexisting. Lastly, we used a nonprobability sampling approach, and our sample was fairly small precluding the ability to examine continuous relationships between FA, alcohol, and marijuana use within each user group separately. Future studies examining the effects of combined alcohol and marijuana use on microstructural integrity of white matter will need larger samples.
