>>83572
>A desensitization on the basis of receptor decoupling, receptor internalization and increased alternative coupling to stimulatory G-proteins have been demonstrated. However, a functional antagonism of the opioid effects seems to be clinically most important, mediated by the activation of NMDA receptors, up-regulation of adenylyl cyclase and nitric oxide synthase. Drugs blocking these mechanisms are the most promising option in the treatment of tolerance. Namely, alpha2-adrenoreceptor agonists such as clonidine and NMDA antagonists such as ketamine or dextromethorphan have been used to minimize tolerance development during opioid treatment.
>http://www.ncbi.nlm.nih.gov/pubmed/15124977
DXM is primarily an NMDA receptor antagonist and this is why it is dissociative.
Theres a lot of strange mythology about DXM online and plateau sigma, related to its sigma receptor effects. I don't know much for sure because its not something thats well studied or understood due to legal issues.
But there is an interesting correlation with astral projection experiences and sigma drugs, ie: DMT, Salvia, Ketamine, Ibogaine, DXM, Herion which have unique myths about hyperspace, k-hole, nodding etc. I believe the sigma receptor has something to do with this experience.
DXM is a non selective SSRI and is known to cause serotonin syndrome in combination with Prozac(fluoxetine)
http://www.webmd.com/drugs/2/drug-6997/prozac-oral/details/list-interaction-details/dmid-2407/dmtitle-fluoxetine-paroxetine-dextromethorphan-and-quinidine/intrtype-drug
I don't think theres any reason codeine would cause SS, mixing those would just make you more tired than average
the experience on DXM is not similar to opiates because the majority of the physical effects are different, because the primary action of opiates is on the kappa, but you might notice they have the same three ring skeleton, because of this and the principle of diffusion, some percent of the time they will just so happen to land in that receptor anyway, especially if there is overflow(you take a lot), but since DXM fits much much better in other receptors it will mostly go there. the speculation about sigma plateau is that sufficient redosing causes the plasma level of metabolized DXO across the blood brain barrier to overload these receptors and the overflow activates maximum sigma dissociation linking (you) into the astral network, they also say polisterix(delysm) slower metabolism helps achieve this.
interestingly the reason salvia often is accompanied by a dysphoria and "fear of impending doom" is because it is an opiate agonist, having the inverse of opiate euphoria, though some people can enjoy that sensation.
>Dextromethorphan's hallucinogenic and dissociative effects can be attributed largely to dextrorphan (DXO), a metabolite produced when dextromethorphan is metabolized by the body.
>Dextromethorphan's euphoric effects have sometimes been attributed to an increase in dopamine levels, since such an increase generally correlates with pleasurable responses to drug. At high doses, dextromethorphan is classified as a dissociative general anesthetic and hallucinogen, similar to the controlled substances ketamine and phencyclidine (PCP). Also like those drugs, dextromethorphan is an NMDA receptor antagonist.
I actually have no idea for sure why DXM makes you hallucinate, but in double blinds people mistake it for mushrooms
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3652430/
Its a very fuzzy subject but i think the salvia-dmt-opiate link is probably really important, its worth noting though that DXM is rather dangerous and can cause seizures if you use it habitually or mix it with other drugs. Ketamine is much safer for mixing and takes nearly an ounce to overdose, but habitual use also ends with kidney problems. I also heard strange things about taking DXM for amphetamine tolerance. Something about dopamine and nueroprotection. The interesting thing about that is how dopamine is related to Parkinson's, which is why meth addicts get shakes. These inter-related effects are rarely studied because its not financially viable for the pharmaceutical industry which relies on reductive logic: treat symptoms, collect insurance, ignore cause.
http://www.dextroverse.org/
https://erowid.org/chemicals/dxm/faq/dxm_faq.shtml
https://erowid.org/chemicals/dxm/faq/dxm_physiological.shtml#toc.9
https://erowid.org/chemicals/dxm/faq/dxm_neuropharm.shtml#toc.10.2
http://www.dextroverse.org/faqs/4-4-what-is-dextrorphan-dxo/