Here are a few scholarly articles on the subject to help ease your concerns.
https://www.clinicalpainadvisor.com/news/ketamine-lozenges-troches-safe-effective-chronic-noncancer-pain-reduced-opioid-use/;
https://consultqd.clevelandclinic.org/low-dose-ketamine-protocol-for-chronic-refractory-pain;
https://pmc.ncbi.nlm.nih.gov/articles/PMC12456614/