Lots of cites in the short wikipedia article:
<a href="https://en.wikipedia.org/wiki/Monosodium_glutamate" rel="nofollow">https://en.wikipedia.org/wiki/Monosodium_glutamate</a>
To paraphrase the wiki, it still won't stop US ad-copy writers from touting "MSG Free!", even for products that already contain glutamic acid.