I take 300mg of Effexor and 15mg of Abilify. Well, I take the generic versions, but the only difference is in packaging. I've never heard of Serotinin Syndrome, however, I do know that Abilify works with my Effexor to help treat my depression and other symptoms (fits of inexplicable anger and episodes of derealization) that Effexor alone wasn't able to treat.