One particularly interesting nootropic for the over caffeinated crowd is l-theanine. This is a smart drug that naturally occurs in teas and some mushrooms. In Japan l-theanine is added to commercial teas, soft drinks and desserts. This substance is generally recognized as safe (GRAS) by the FDA and is available in the US through the supplement market.
50mg – 250mg is the normal dosage range. Reports of stomach irritation occur at dosages over 400mg. L-theanine is water-soluble. I normally dissolve 100mg powdered l-theanine in water and take up to four times daily.