Theanine is a natural amino acid-like relaxant found in green tea. Buspar is generally regarded as not working, so that could explain that. Whether theanine alone will help only experience will tell; usually natural remedies are used in combination for best results. Try a book called Natural Highs by Hyla Cass, a colleague of Dr. Gould's.
I am sorry, I don't know anything about that medication so suggest you search a reputable medical search engine, the kind you might find on webmd or government site.