I find that the brain fog does occur with memantine. But it is temporary. Memantine, IIRC in addition to its actions as a low-affinity, long acting uncompetitive, voltage-sensitive (I.e it only binds to the NMDAr ion channel pore whilst it is in the open state, its an open-channel blocker that requires the channel to be open (thus the receptor firing) before binding and exerting its effects as an antagonist) is also an alpha7 nicotinic acetylcholine receptor antagonist. Antagonists at alpha7 nAChRs rapidly induce a compensatory upregulation, whilst agonists are nootropic but also, cause a compensatory downregulation with continued use, at least with high potency ones and high doses. Galantamine, the anticholinesterase derived originally from snowdrop plants (Galanthus nivalis) also unlike most other (and likely all other clinically used ones) acetylcholinesterase inhibitors, also has effects as an alpha7 nicotinic ACh receptor agonist, although the initial peak in its nootropic effects seems to fade back down to just somewhat more effective than other anticholinesterases as a nootropic with continued use, esp. at high doses.)
With memantine, first the receptors (nAChRs of the alpha7 neuronal type that is) are blocked, and in response, the level of expression of alpha7 nAChRs is upregulated causing initially a decrement in cognition/some brain-fog, and then quite quickly this turns into a positive, nootropic effect instead of a dulling one. As for its general effects, I've taken it in doses most doctors would faint with shock at, such as fr.ex an around 200mg intravenous dose (coadministered with an opioid, in the case of the opioid, 6-monoacetyldihydromorphine) and it blew my fucking head off. That shot had me literally staggering to walk for over half an hour to 3/4 of an hour just with the initial opioid rush, not the high, just the rush, it just kept going and going and going, and going hard (the dose was 300mg of the 6-AcO-DHM combined with the memantine (unsure what salt it was) so a solid dose, even for someone with my opioid tolerance (I'm a chronic pain patient with fucked up joints and trochanteric bursitis, both sides, along with some nerve damage to my leg that causes a permanent contraction of the calf muscle with much impaired ability for the corresponding relaxation response to occur and/or propagate, causing a severe spasm, that I need daily, high-dose tizanidine (a real beast of a muscle relaxant, acting as an agonist at alpha2 adrenergic autoreceptors) to deal with, also taking morphine and oxycodone in doses the other doctors stay just short of outright complaining and bitching at me (most of them at least, some of them do have a go at me for having the prescription) and have had to take the opiates for a long time, and the muscle relaxers for years, since the surgery I had done to attempt (and fail miserably) to fix my fucked up knee joint, since it was the surgery that inflicted the nerve damage for the most part at least.
And memantine for me, works WONDERS. I'm still fighting my doctor more or less to try and get a script for it. But when I can get hold of it, its a literal lifesaver for me, difference between functioning and not, after getting fucked over, locked up for something I essentially was not responsible for at the time, and put through court whilst in frank DTs, straight from the ER and by the time of being in a courtroom, in no way able to even try to present a defense, duty 'lawyer' just waved it all on and didn't give a damn in my defence. Not a tinker's shit. And I should not of course have been put through a legal issue of any kind whilst physiologically, medically incapacitated. Due to dependency on barbiturates, I had enough to taper slowly, and would have done, had it not been for the sudden arrest, and had to go cold-turkey, unaided, bar the initial ending up in intensive care, which did some major fucking over of me. And major memory/cognition issues, and going from being (born) dyscalculic to now nearly acalculic. Not quite but not terribly far off. But memantine..damn, it literally reverses everything wrong.
And I've taken it and found it pretty damn effective at 100mg/d or even that dose BD. Memantine is...like manna from heaven for me. Little dissociative type 'hole' effects, save when taken in a thoroughly massive dose, especially intravenously. Although my preferred route was to plug it in solution for higher BA and greater rapidity of onset. But it IS possible to enter such a state, although it lasts a damn long time, and you better set aside at least a full day and possibly night also if taking it in the morning at such a dose. Seems to help lessen the frequency of the seizures I have (for which my usual medication, is, albeit off-label in my country for that indication, save in acute alcohol detox for inpatients, is chlormethiazole [heminevrin] which works well, and will stop a seizure dead in the water, and whats more, do it FAST) but memantine also lessens the frequency of the seizures and renders them less prone to resulting in complete incapacitation to a point where despite knowing whats about to kick off, I can't grab the chlormethiazole bottle in a two-handed grip, holding on for dear bloody well life, and manage to dump a cap or two of the stuff down my neck, at least, down the part of it thats inside me) before the damnable things turn totally atonic, complete paralysis of voluntary muscle, breathing excluded, and then turning myoclonic after a while of being stuck there, being able to see, feeling as if I were being repetitively shocked with a high-voltage source to my bare, de-skulled brain, or a car battery being plugged into my spinal cord.
Your turning to nicotine gum is interesting, and makes quite a bit of sense, but ideally if you were to stick with the memantine and let the alpha7 nAChRs fully play out their upregulation and suck the brain fog up briefly, it MAY work better, can't say for sure, since LC uses an E-cig already, and he does enjoy his cigars (toking lazily on a nice juicy half corona right now, whilst slurping up some info about borane chemistry
