Gwern, regarding Modafinil - have you looked into the interaction with COMT polymorphisms?

I read somewhere that carriers of the Val158Met polymorphism (mutation, under positive selection, reduces breakdown of dopamine in frontal lobe, increases working memory) do not see positive effects from Modafinil, while the ancestral Val carriers do see benefits.

I'll try to track down the study and post it when I have more time.