http://en.wikipedia.org/wiki/Methylene_blue

"...Methylene blue is a monoamine oxidase inhibitor,[4] and if infused intravenously at doses exceeding 5 mg/kg, may precipitate serious serotonin toxicity, serotonin syndrome, if combined with any selective serotonin reuptake inhibitors (SSRIs) or other serotonin reuptake inhibitor (e.g., duloxetine, sibutramine, venlafaxine, clomipramine, imipramine).[5]

TauRx Therapeutics has reported that methylene blue (methylthioninium chloride), under the tradename rember, may provide a way of halting or slowing the progression of Alzheimer's dementia.[6] However, the formulation used was different from that commonly available as a medicine and caution has been expressed about use of methylene blue as a treatment for Alzheimer's.[7] TauRx Therapeutics has suggested that the mechanism by which methylene blue might delay or reverse neurodegeneration in Alzheimer's disease is as an inhibitor of Tau protein aggregation. While methylene blue arguably has an effect on Tau aggregation, it also has an effect on mitochondrial function which is likely to play an important role. In vitro studies suggest that methylene blue might be an effective remedy for both Alzheimer's and Parkinson's disease by enhancing key mitochondrial biochemical pathways. It can disinhibit and increase complex IV, whose inhibition correlates with Alzheimer's disease. Methylene blue might also delay senescence as one study has shown that it extended the lifespan of IMR90 fibroblasts by more than 20 population doublings..."