Amino acids are the building blocks of protein molecules, relatively simple natural substances that are the first breakdown products of the digestion of proteins. There is no need to take mixtures of amino acids as nutritional supplements, no matter what fitness instructors, bodybuilders, and athletes tell you. If you eat adequate protein, you will have all the amino acids you need and probably more. Single amino acids are another matter. There are some single amino acids that have been used to treat various health problems. These include L-tryptophan, L-arginine, L-lysine, among others. Take single amino acids for treatment of particular conditions. Take them only on an empty stomach and stop using them if you do not notice any beneficial effects after a reasonable trial, say two to four weeks.