Think there is tolerance, but little to early to tell, I have been increasing the dose each time as I have got a bit braver, at first was veryncatiousnwith a 20mg but have taken 200mg and also inhaled smaller doses, hmakes you cough. I want to thoroughly test this , and find out tolerance issues and also withdrawal problems, I am prepared for both and accept the unknown side effects, I have been dip sticking my urine and monitoring blood pressure, but still there is a risk as no real human trials, they have tested up to 1mg/kg in mice but no way of knowing the relevant human dose but I'm guessing its higher, no evidence to back this up but we have bigger brains, more synapses and receptors for it to work on. I'm also on memantine so some of my NMDA receptors are blocked, hopefully protecting me from risks of glutamate hyperactivity.
You realize that human doses in terms of mg/kg are much lower than rat doses, right? I did the calculations a page or two back, and the largest dose tested in a single rat study is equivalent to roughly 200 mg in humans.