May Use in the headline would be better written as Regularly Use, to reflect the article.

    The tendency to use cannabis is associated with genes linked to
    impulsive behavior, obesity, schizophrenia and bipolar disorder,
    among other traits, according to a study 

The article confuses me because it seems to be presenting cannabis use as purely recreational. Medical use isn't mentioned at all - so we don't know where medical users fit in this study.

Nearly every cannabis user I know is using it for pain, insomnia and/or anxiety.