LONGECITY

I have gut issues and I was wondering are there any drugs that work well for anxiety which have been shown to be absorbed in the stomach or big intestine well? I am looking at agmatine and Amantadine currently which have NMDA antagonistic actions but I'm not sure on their absorption or effectiveness. Or if the drug is injected. And please point out their mechanism. I have tried memantine and it works well and absorbed do the other two drugs absorb the same? Memantine is too harsh on my gut.