I don't know enough to evaluate this advice, but the word "histamine" caught my eye.

There are antidepressants that, as I understand it, are antihistamines. For example, imipramine. I wonder what it means if you have an adverse reaction to such a drug, and something resembling schizophrenia as well.

I tried prescription memantine, both the generic and XR formulations. The brain fog startup side effect never went away for me, so I had to quit. I've never found a supplement that has actually done anything.

Did you taper 2.5 mg at a time every 3-4 days until taking 5-10 mg? Also add selank. Have you ever tried chelated/TRAACS magnesium? What else have you tried?

Do you have any nutrient deficiencies? Ever looked into nutrient tests like NutrEval? A comprehensive hormone panel? Thyroid panel? Genetic testing?

I also tried Memantine, my verbal fluency took a serious nose dive, I was unable to follow simple instructions. I slowly tapered up, much slower than 2.5 mg at a time.

It helped in some other areas, but not being able to do simple tasks nixed it for me.