I use NOW Foods Branch Chain Amino Acid Powder. It's 100% pure with no gluten, wheat, soy, sugar, or nut/legume ingredients that are often times found in BCAAs. It does contain TRACE amounts of milk, but so low that they can round up and legally say it's 100% pure. One caveat though, raw BCAAs taste terrible. I mix it in with my protein powder to make it palatable.