It's complicated and depends on your body weight. You always want to do a low dose on your first trip, and then increase gradually with each new trip. Please note that DXM starts becoming toxic around 25 to 30 mg/kg! Be careful!
NMDA receptor antagonists
Dissociatives are a class of hallucinogen, which distort perceptions of sight and sound and produce feelings of detachment - dissociation - from the environment and self. This is done through reducing or blocking signals to the conscious mind from other parts of the brain. Although many kinds of drugs are capable of such action, dissociatives are unique in that they do so in such a way that they produce hallucinogenic effects, which may include sensory deprivation, dissociation, hallucinations, and dream-like states or trances. Some, which are nonselective in action and affect the dopamine and/or opioid systems, may be capable of inducing euphoria. Many dissociatives have general depressant effects and can produce sedation, respiratory depression]citation needed[, analgesia, anesthesia, and ataxia, as well as cognitive and memory impairment and amnesia.]citation needed[
Magnesium in biology
NMDA receptor antagonists are a class of anesthetics that work to antagonize, or inhibit the action of, the -aspartateD-Methyl-N receptor (NMDAR). They are used as anesthesia for animals and for humans; the state of anesthesia they induce is referred to as dissociative anesthesia. There is evidence that NMDA receptor antagonists can cause a certain type of neurotoxicity or brain damage referred to as Olney's Lesions in rodents, although such damage has never been conclusively observed in primates like humans. However, in adolescent cynomolgus monkeys that were injected daily with the non-competitive NMDA antagonist, ketamine, there were some definite neurologic deficits observed.
Several synthetic opioids function additionally as NMDAR-antagonists, such as Meperidine, Methadone, Dextropropoxyphene, Tramadol and Ketobemidone.
Health Medical Pharma
Magnesium is an essential element in biological systems. Magnesium occurs typically as the Mg2+ ion. It is an essential mineral nutrient (i.e., element) for life and is present in every cell type in every organism. For example, ATP (adenosine triphosphate), the main source of energy in cells, must be bound to a magnesium ion in order to be biologically active. What is called ATP is often actually Mg-ATP. As such, magnesium plays a role in the stability of all polyphosphate compounds in the cells, including those associated with the synthesis of DNA and RNA.
Over 300 enzymes require the presence of magnesium ions for their catalytic action, including all enzymes utilizing or synthesizing ATP, or those that use other nucleotides to synthesize DNA and RNA.