Warning!
7% of all Caucasians (the rate varies with other ethnic groups) have a genetic mutation known as CYP2D6 deficiency. This is a liver enzyme that is critical in metabolizing DXM. It turns out if you are one of the unlucky 1 in 14 or so that have this mutation, dextromethorphan at recreational doses will likely be an unpleasant, psychotic nightmare.
WAAAH!!!! HAHAHAHAHAHAA!!!!!!!!!!!!!
Fourth plateau (15-30 mg/kg; although dosing beyond 20 mg/kg is not advisable, nor needed, for most people.)
At this level, total mind/body dissociation occurs. The tripper loses some or all contact with his external senses, and is unable to move or respond to stimuli. He/she is in his own imaginary universe, while the sitter is watching to make sure the tripper doesn’t choke on his/her own vomit, go into seizures, or otherwise need medical attention. As for what the experience is, anything is possible. Some have hallucinated contacts with god(s), alien beings, seeing bizarre worlds, and other strange effects, along with completely irrational thinking. Dosage at this level is far from safe, and should done only by those who have taken dextromethorphan at third plateau levels before, and have done so with positive outcomes. Even in that case, considering the known risks of dextromethorphan with respect to brain damage (and the fact this risk is greatest at fourth plateau levels), remember the brain you may be frying will be yours. Thus, don’t even think about use at these sorts of doses unless you fully understand and accept the high risk involved. Also, NEVER, EVER use at this level without a SOBER trip sitter.
QUICK! Someone go drink 8 big bottles (10 oz) of Nyquil and make contact with god!!!! Of course you will have ingested 4.7 grams of ephedrine and that would be bad...