There are arcane rules about what can be described as what on a label. I believe that in the U.S. if you synthesise something from petrochemicals you have to call it "artificial flavor" but if you synthesise it from plants or animals you can call it "natural flavor". But it doesn't necessarily make any difference to the toxicity of something where your raw materials for the lab come from.
Here's the FDA on MSG:
Questions and Answers on Monosodium glutamate (MSG)FDA requires that foods containing added MSG list it in the ingredient panel on the packaging as monosodium glutamate. However, MSG occurs naturally in ingredients such as hydrolyzed vegetable protein, autolyzed yeast, hydrolyzed yeast, yeast extract, soy extracts, and protein isolate, as well as in tomatoes and cheeses. While FDA requires that these products be listed on the ingredient panel, the agency does not require the label to also specify that they naturally contain MSG. However, foods with any ingredient that naturally contains MSG cannot claim “No MSG” or “No added MSG” on their packaging. MSG also cannot be listed as “spices and flavoring.”
I would read that as saying that if you added some "hydrolyzed vegetable protein" or something similar to a vegetable juice to give it a kick, while MSG would be present, you wouldn't have to declare it on a label.
If you usually find you get that reaction when you've had MSG, then I'd be fairly suspicious of that product.
I'd also have thought that if you do get a "serious craving" for it, then - paradoxically - it might be the MSG that you're craving.
I think people can and do crave things they're in need of - that's a natural response that helps us navigate our way through our environment and find the nutrition we need. However, those responses can get hijacked. There's plenty of evidence that food companies spend an astonishing amount of money on adding small amounts of this or that to a food in order to hook people on it. The word seems appropriate: it is almost analogous to the response some people seem to get to drugs, alcohol, tobacco, or other substances they have problems with.
Those adverts where they say things like, "Bet you can't eat just one," rather give the game away.
When it comes to "food addiction" it seems likely it's an error to think that the problem is "fat, sugar, salt" as one rather silly popular book had it. People are much more likely to be responding to flavourings than to macronutrients or salt. Of course, if you lace a big bag of corn chips with flavourings that make the buyer keep coming back for more, the end result of that is that he gets a huge dose of one macronutrient - carbohydrate - that he definitely doesn't need in excess and that will spike his insulin and generally do him no good.