MSG is Monosodium Glutamate, the sodium salt of glutamate. Glutamate is an amino acid common in food, I assure you you eat tons of glutamate on a daily basis. There's nothing inherently unsafe about it, and your body knows exactly what to do with it. In fact, your body is literally made with it.

That said glutamate is a neurotransmitter, so yeah you probably shouldn't inject large quantities or anything.