It is considered safe at low quantities, but no sufficient studies have been conducted concerning higher quantities. For more information, have a look at the statements by the US FDA:
[https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/CFRSearch.cfm?fr=172.530&SearchTerm=disodium%20guanylate](https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/CFRSearch.cfm?fr=172.530&SearchTerm=disodium%20guanylate)

There are studies that hint towards toxic effects nevertheless, see for example:
[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5938543/](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5938543/)
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