There are about 500 amino acids in nature. Twenty of these are amino acids that serve as building blocks for proteins in the human body. L-theanine is a free amino acid that does not belong to the essential amino acids, nor to the non-essential amino acids and is not incorporated into body proteins. Also called ?-glutamylethylamide or 5-N-ethylglutamine, theanine is similar to glutamine but has unique properties. In nature, it occurs almost exclusively in the tea plant (Camellia sinensis) and contributes to the taste of tea. It is absorbed quickly after ingestion and can be taken shortly before going to sleep or in the morning and combined with caffeine.