DXM should not be used (either recreationally or at normal dosage levels)
by people who are taking a monoamine oxidase inhibitor (MAOI, rhymes with
“wowee”) - either a prescription MAOI or a recreational one such as
harmaline. Note that there is considerable confusion among drug users about
what is and isn’t a MAOI. MAOIs include a few drugs prescribed for
depression and Parkinson’s disease, and a few rare recreational drugs
derived from exotic plant sources (harmine and harmaline, from Syrian Rue
and Yagé, for example). ProzacTM, MDMA, cheese, beer, SeldaneTM, etc., are
not MAOIs - they are things to avoid when taking a MAOI. If you are taking
a prescription MAOI you will almost certainly know, as your physician will
have (hopefully!) told you to avoid eating aged cheeses. Combining DXM and
a MAOI has been fatal (3)!

Fluoxetine (ProzacTM) is a cytochrome P450-2D6 inhibitor (39) and will
change the characteristics of a DXM trip somewhat, increasing the ratio of
DXM to DXO. Other P450-2D6 inhibiting drugs, which include many
antidepressants, will probably do the same; see Section 15.1. The duration
of the trip may be greatly extended by P450-2D6 inhibitors; some users have
reported effects lasting 12 to 24 hours past the normal duration. The
potency of DXM may also be enhanced via other mechanisms by fluoxetine
(40).

Combining DXM with the antidepressants Desyrel (trazodone) or Serzone
(nefazodone) has been reported to cause liver damage!

One user reported that combining DXM with bupropion (Wellbutrin[tm])
resulted in a prolonged (3+ day) hangover and an increase in adverse side
effects.

Fluoxetine and other SSRI antidepressants, as well as tricyclics and
lithium (and of course MAOIs) may interact with DXM to cause serotonin
syndrome (see Section 6.2.9). This condition, although rarely fatal, is not
terribly pleasant. Vascular disease may increase the chance for serotonin
syndrome with DXM + antidepressants (364), and other disease conditions may
do so as well. Some DXM users who have taken DXM while on antidepressants
have reported unpleasant reactions that sound a lot like serotonin
syndrome, so you might want to watch out. Some of the symptoms of serotonin
syndrome include muscle rigidity, confusion, diarrhea, incoordination,
low-grade fever, sweating, muscle tremor, mania, agitation, exaggerated
reflexes, and nausea.

Do not take DXM with the diet drugs phentermine, fenfluramine, or phen-fen;
this combination can also cause serotonin syndrome.

DXM should not be taken (recreationally or at normal dosage levels) with
the prescription antihistamine terfenadine (SeldaneTM). This combination
has been fatal (41). Terfenadine has been implicated in other drug
interactions, incidentally. The reason for this interaction seems to be
that terfenadine, which is normally metabolized by a P450 enzyme, induces
heart irregularities when it builds up. DXM may saturate the P450 enzymes
that normally metabolize terfenadine. Incidentally, this probably applies
to other non-drowsy antihistamines, such as ClaritinTM and HisminalTM as
well; avoid combining them with DXM.

Some people find that nicotine (cigarettes) causes severe nausea when
combined with DXM. Others have noticed a general increase in physical
discomfort and “bad trips” from combining the two. Some research has
suggested that cigarette smoke inhibits monoamine oxidase (378,379) in
which case cigarettes could greatly increase the chance of unpleasant side
effects.

The four dosage plateaus can be divided into two groups based on a certain
degree of similarity: the lower plateaus and the upper plateaus. The lower
two plateaus share many features and some of these will be considered here.
A generalization would be that the lower two plateaus are more
“recreational” than the upper plateaus. Specifically, they have
considerably less hangover, do not generally involve serious disruption or
breakdown of sensory processing, and are more similar to other intoxicants.

DXM in the lower two plateaus has been compared to a cross between MDA and
alcohol. It tends to intensify emotional responses and feelings of meaning
from external events. At the lower plateaus there is usually enough motor
control to be able to engage in physical activites (although, like MDMA and
MDA there are reasons why you may not want to, including dehydration and
overheating).

Most find sensory input is still understandable, although there are
peculiar changes which will be discussed below (notably flanging). At the
lower plateaus it is still possible to interact extensively with the
outside world, and one can watch and follow reasonably complex plots in
movies, and have complex conversations.

Although DXM is in many ways not a good “casual” drug most people have used
it without adverse effect at the lower plateaus. Interestingly, many people
who have use DXM at the upper plateaus eventually find that the lower
plateaus no longer offer much enjoyment. There are a lot of potential
reasons for this (see Section 7.6); I think most of it is simply that DXM
at the upper plateaus changes one’s expectations about its effects and
gives one familiarity with its memory inhibition.

This is a difficult question to answer, because DXM’s effects tend to vary
widely depending on the person, their set and setting, other drugs, their
physiology, and so on. DXM, probably more than most drugs, tends to exert
its (recreational) effects in separate stages or “plateaus”, rather than
being linearly dose-dependent. Within a given plateau, a given set of
effects will occur (at a roughly dose-dependent strength). On the other
hand, once the next plateau is reached, the feeling may change entirely. A
reasonable analogy is water - it exists in three states (solid, liquid, and
gas) which all can exist at varying temperatures (e.g., hot water and cold
water), but which have different characteristics.

DXM and its metabolite, dextrorphan (DXO), produce different sets of
effects. Normally, DXM is converted mostly or entirely into DXO, but with
recreational doses, the conversion enzyme (P450-2D6) may saturate, leaving
a mixture of DXM and DXO. Furthermore, another of DXM’s metabolites -
3-methoxymorphinan - can also block this enzyme, so that taking divided
doses leads to more DXM and less DXO than taking a combined dose of the
same amount.

DXM’s effects are in some ways much more subtle than DXO’s. Whereas DXO
produces a heavy “stoning” or intoxicating effect, DXM by itself is only
lightly intoxicating. DXM, however, can alter the thought processes,
leading to highly abnormal, psychosis-like mental states. It is possible
that DXM, via sigma activation, may induce a mental state similar to that
of schizophrenia. Whether or not this is fun to you is, of course, up to
you.

DXM seems to exhibit at least four definable plateaus based solely on
dosage, and an additional plateau is notable from a specific dosing regimen
(see below, Section 5.9). I previously listed three plateaus; then four;
now I’m listing five (although “Plateau Sigma” doesn’t occur at dosages
higher than the fourth plateau). Evidently, dosages above the fourth
plateau lead to full anaesthesia, psychosis, coma, and/or death.

Not everyone notes distinction between the first and second plateaus, or
between the third and fourth plateaus. Others suggest that each effect of
DXM has a dosage level at which it starts, and (in some cases) a dosage
level at which its effects are no longer noticeable (being overpowered by
other effects). Some people will disagree with this classification method,
but I think this is the best way to represent DXM’s effects. Both the third
and fourth plateaus have significant dissociative characteristics, much
like ketamine.

The most important thing to keep in mind is that the effects in different
plateaus are often very different. For example, on the first plateau, DXM
tends to have a stimulant effect. Upon reaching the second plateau,
however, the stimulant effect may no longer be present.

The beginning of the comedown off of a DXM trip can come abruptly. Often,
the user will know when it’s starting to end by noticing the return of
normal sensory processing. Coming down from there may take a significant
amount of time. A second DXM trip too soon after coming down is not a good
idea due to the potential for side effects and psychotic episodes (227).
Wait at least three days and preferrably two weeks between each DXM trip.

The following table can be used as a general guideline for the plateaus.
For convenience I give example dosages in gelcaps and 3mg/ml syrup for 75kg
and 150lb adults; adjust up or down by the amounts indicated per 10kg or
25lb. Calculating with the mg/kg is more accurate, but it’s easy to make
mistakes when using non-metric measures. These dosages are as DXM
hydrobromide.

Dosage will vary considerably from person to person, by as much as 5 times!
Also, these mg/kg figures should evidently be adjusted down for higher mass
(e.g., maybe 6mg/kg to 13mg/kg third plateau for a 150kg adult). Note that
kg = pounds * 0.45.

I have included a new category in this table: “Usenet Suggestions”. This is
a combination of suggested dosage guidelines from Usenet, and may more
accurately represent the plateau dosage of DXM in regular users (the
original plateau levels were based mostly on occasional users).

Table 1: DXM Plateaus and Dosages

Plateau First Second Third Fourth
Dosage Range
(mg/kg) 1.5-2.5 mg/kg 2.5-7.5 mg/kg 7.5-15 mg/kg >15mg/kg
Usenet Suggestions
(mg/kg) 2.7 mg/kg 6.4 mg/kg 9.4 mg/kg 18mg/kg
Gelcaps (30mg) for 4 to 6 6 to 18 18 to 37
75kg adult gelcaps gelcaps gelcaps >37 gelcaps

Adjust per 10kg 1/2 to 1 1 to 2.5 2.5 to 5 5 gelcaps
gelcap gelcaps gelcaps
Gelcaps (30mg) for 3 to 5 5 to 17 17 to 34
150lb adult gelcaps gelcaps gelcaps >34 gelcaps

Adjust per 25lb 1/2 to 1 1 to 2.5 2.5 to 5.5 5.5 gelcaps
gelcaps gelcaps gelcaps
Syrup (3mg/ml) for
75kg adult 37 to 62 ml 62 to 187 ml 187 to 375 ml >375 ml
Adjust per 10kg 5 to 8 ml 8 to 25 ml 25 to 50 ml 50 ml
Syrup (3mg/ml) for 2 tbsp to 2 2 oz to 5.5 5.5 oz to 11
150lb adult oz (1/4 cup) oz (2/3 cup) oz (1 1/3 cup) >11oz

Adjust per 25lb 1 tsp to 2 2 tsp to 1 oz 2 tbsp to 2oz 2 oz
tsp (1/8 cup) (1/4 cup)

The specific effects at each plateau will be listed according to the
following categories: Sensory, Cognitive/Emotional, Motor, and Memory.
Additionally, the lower two plateaus are considered together, as are the
upper two plateaus.

This section discusses some of the effects you might expect to feel if you
were to use DXM recreationally (which I recommend against, of course). The
effects listed are generally positive, and reflect the results of people
who have positive experiences with DXM.

Some people have negative experiences with DXM! For these people, the DXM
“trip” may just be several hours of dizziness, nausea, hot flashes, and
confusion, with several days of hangover. This is the main reason why most
DXM users suggest starting with a first plateau dose.

As DXM itself, probably not; nobody bothers to look for it. There has been
some anecdotal evidence that DXM can cause false positives for opiate
tests, but one paper (374) disputes this. There may be more reliable
evidence that DXM can cause false positives for PCP and possibly cocaine.

So keep this in mind before using DXM if you have to take a drug test. If
worse comes to worse, you can always claim you had a bad cold, and ask them
to do a test which will discriminate between opiates and DXM. Good luck!

A variety of substances have been used as topical anaesthetics to numb the
throat, including phenol and methol. These have no recreational use
potential (and in general are highly toxic in overdoses).

Opiates are of course still used as cough suppressants; the most common is
codeine, which is still used for severe coughs (although some research
suggests it is no better than DXM). Other opiates have been used for severe
cough. As an interesting bit of trivia, heroin was first marketed for cough
suppression.

The recreational effects of opiates are fairly well known, and are in any
case beyond the scope of the DXM FAQ.

Noscapine is a natural ingredient in opium, and is related to papaverine.
It doesn’t seem to have any opiate-like effects (other than cough
suppression) and is not constipating. It may be a NMDA/sigma ligand like
DXM. Adverse effects and effects of overdose include drowsiness, dizziness,
headache, nausea, allergic rhinitis, conjunctivitis, and skin rashes. I
have no idea whether it has recreational effects at high doses, but I
wouldn’t advise finding out. Oral adult dose is 25mg-50mg 3-4 times daily.

There are other cough suppressants available, of course, but none of them
are likely to take the place of DXM.

Marijauna and DXM is a frequently used combination, albeit one which has
seen little research. Competitive NMDA blockade enhances marijuana
catalepsy (210), and conceivably noncompetitive blockade would as well.
Dizocilpine, a dissociative used in research, decreases the analgesic
effects of marijuana (214), and causes downregulation of anandamide
receptors (THC receptors) (218).

Dissociatives may block the depletion of 5HT (serotonin) caused by MDMA
(ecstasy) (241). However, there is also the potential for hypertensive
problems, so I wouldn’t advise this combination. Methamphetamine produces
vacuolation of neuron terminals due to a collapsed vesicular proton
gradient (181) (translated into English, this means that speed damages
brain cells by breaking open the little bubbles of neurotransmitters inside
the cells). However, dizocilpine (and presumably other dissociatives) may
prevent this (219). It also seems to block methamphetamine induced 5HT
depletion (241).

Antidepressants and dissociatives seem to interact as well, not necessarily
in a good way. Both desipramine and dissociatives increase prefrontal lobe
dopamine activity; the combination is highly synergistic (277). Even worse,
dissociatives may actually reverse the antidepressant effect (229).
Dizocilpine reduces 5HT2 receptor density (212), and increases 5HT binding
in the hippocampus and striatum (252). On the other hand, one paper found
that dizocilpine helped antidepressants in some tests (245,250).

Finally, dissociatives block tolerance to many drugs, including alcohol
(232), cocaine (247), nicotine (249), and morphine (248).