Well when I was on memantine, I've taken it both separately, dosing them on the same day, etc. just not in the same syringe at the same time, and taking as the memantine version of a speedball.
The 'memantineball' thing, that, helped with tolerance, etc. but it didn't take the addictive tendencies away as much as it did taking the two separately (the opioids being morphine, oxycodone as general purpose, although the morphine has ended up as dibenzoylmorphine, di-n-butyroylmorphine, diacetylmorphine and dipropionylmorphine, the first three of those, to me, are pretty bland, but dipropionylmorphine, oh my god. JACK-POOOOOTTT

Either DPM, or the ester 6-monoacetyldihydromorphine, administered in the same rig with high dose memantine, reliably blows my ass off so damn hard, I'm surprised people aren't asking why my ears have a perineum.
When using pain meds more...responsibly, shall we say, more in line with what the doctor would at least hope and plead for, if not order, and hope he'd get, in terms of use
Then dosing IM, where there isn't that huge, highly reinforcing rush, the slower absorption lessening the rush, but still allowing it to be useful, in the case of morphine, because my script, I got transferred to morphine and lower dose oxy, the latter, IR capsules at a lowish dose, repeatedly through the day to serve as breakthrough and help the pain patient's equivalent of blood sugar dipping post-breakfast, in the afternoon after snack, after supper, etc. etc., and keep plasma levels consistent enough to not frequently start overheating,feeling like I'm about ready to strangle the neighbor's cats with piano wire twisted round a pair of forks for miaowing too loud (I'm joking, there, I love animals. As long as they aren't disease carrying parasites which fly onto, or latch onto, one's body in order to plunge a blood-slurping stylet into same and start sucking my jealously-guarded vital pink juices out of it, I'm an animal lover. Those that are can expect a quick, vicious stomp of a boot heel, or a cigarette lighter and a can of deodorant, full of flammable alcohol and butane pointed their way, and to become crispy critters faster than you can say, in a really tiny, high pitched voice 'saaavee meeeeeee.....my FACE IS MEEELLttttiiiiNNggGGGgg!!.........;'
And besides the neighbors are out, touring the world on holiday, have been for most of the year. Too bad, I've a hunch the girl might have spectrum tendencies and shes kinda hot....
Anyway..

When I was IMing the morphine and plugging or insufflating the oxy IR, and the memantine was being taken orally, I found the opioids still killed pain, as they ought to, somewhat better in fact, the tolerance I HAD at the time, was being severely beaten and slapped around, brutally sodomized if it dropped the soap in the shower with tolerances to any other medication; to the extent that I'd not have dared keep on doing 1g or more shots of morphine, even as several shots at once, divided among several muscle groups, for fear I might OD. And if that opioid tolerance walked into the shower and found the tiny, tiny weedy tolerance if any, from benzos, used at most 2-3 times, in high doses, a week, it'd find a nitrazepam tolerance built like an anorexic, which cried and begged for general anaesthesia to get it's prison tattoes done, could have shoved that opiate tolerance to the ground whilst it looked for that soap, and shoved a clenched, stick-thin, anaemic-looking fist on a match-stick arm out of a chloride ion channel in the center of a nearby GABAa receptor and rammed said fist right up the MOR agonist tolerance's own ass so far it could have it's teeth picked after a meal, by the fist up it's ass. Without having to reach with the toothpick
And slowed development of acquiring more tolerance too, also, it made opioids, still enjoyable, no less than they were before at the moment of dosing, and I'd still continue to function, not to withdraw, etc., still be out of pain in my knee and hips, the eye that got burned (you don't even want to know), but whilst doing their jobs, rather than the initial euphoria on dosing, it'd just be sitting in the background, politely, not always screaming 'more! more! MOR wants MORE!', and that I found I actually had to go and REMEMBER to go to the pain med boxes, prep a shot, stick it in the muscle, enjoy while the initial glow made smoking a cigar feel really, really satisfying (somewhat less, though in the case of the cigar on top while on memantine), in fact it helped me switch to an E-fag too and only smoke cigars now, with my opioid doses, where I used to smoke rollups, and a lot of them,30g baccy would last me a few days.
But I would, I'd actively, deliberately have to think to myself 'my body will require it's opioid ration soon, so lets go up and get that done', rather than the opioid's reinforcing nature prod me to go get some.
As for codeine, you mention, it is a very weak opioid, and as it is of more or less only much use orally, as a prodrug, there is also a sizeable delay between taking a dose, and its being metabolized to something active, so there is never that instant hit-Ka-CHIIING$$$$!!!$$$ type of mental salience increase associating the prick of a hollow metal spike with instantaneous supra-maximal euphoria. Some opioids might be able to push in front of the rest of the line, waiting to board 'the ride of your life' and use strength to bully their way to the end, but codeine just has to sit there on the benches, waiting it's turn, and when it gets there, take the kiddie's slide. Hell even drinking too much grapefruit juice can bitch-slap codeine further back than it started.
And don't worry about 'damn' etc.You'll probably see far worse here. Possibly when that wanker dresden shows up and cops a face full for being a bumptious little tit
