112 Dextromethorphan
phan can relieve abstinence symptoms experienced byheroinaddicts. Such
results do not demonstrate whether dextromethorphan has cross-tolerance
with all the drugs just named, allowing it to be substituted for any of them;
their withdrawal syndromes all include elements mimicking the common cold
and flu, and dextromethorphan may simply be able to relieve flulike symp-
toms regardless of cause.
Rats that dose themselves with intravenouscocainehave shown less interest
in that drug after receiving dextromethorphan, but the meaning of that re-
duced interest is unclear: Does dextromethorphan promote abandonment of
drug use, or do the animals find dextromethorphan so preferable that cocaine
cannot compete?
Drug interactions.Dextromethorphan can boost pain relief actions of mor-
phine, allowing patients to use less of that opiate. Research has also found
that dextromethorphan does not boost euphoria or dependence produced by
morphine, leading one investigator to conclude that morphine’s illicit attrac-
tions are not increased by dextromethorphan.
Dangerous interactions may occur if dextromethorphan is taken along with
MDMA, with monoamine oxidase inhibitors (MAOIs, found in some antide-
pressants and other medicine), or with serotonin uptake reinhibitors (a type
of antidepressant). When taken with dextromethorphan the latter substances
could provoke the “serotonin syndrome,” a potentially fatal emergency in-
volving muscle tremors, heartbeat and blood pressure abnormalities, changes
in mental state, and loss of consciousness. In rats the drug reduces effects
produced by PCP. Dextromethorphan can cause false positives for PCP in
urine tests, but an experiment failed to produce positives for opioids.
Cancer.Not enough scientific information to report.
Pregnancy.The drug has been widely used for decades without report of
congenital malformations. After chicken embryo experiments in the 1990s sug-
gested that dextromethorphan might cause birth defects, a study in Canada
compared women who used the drug during pregnancy with those who did
not and found no increase of congenital defects in the drug group. A study
looking for birth malformations in Spain found none that could be attributed
to dextromethorphan and concluded that normal medical used of the drug
did not produce birth defects. Those negative findings have not surprised
experts familiar with drawbacks in using chicken embryos to test for birth
defects; chicken development can be harmed by conditions having no effect
on humans, and chicken embryo tests are no longer accepted as indicating
human risk of birth defects. Several human studies, however, have found a
slight increase in risk of birth defects among pregnant women using dextro-
methorphan. The risk is close to negligible, but, as one authority points out,
that is not the same as zero risk. The small chance can be reduced to zero by
avoiding the drug during pregnancy.
Additional scientific information may be found in:Darboe, M.N. “Abuse of Dextromethorphan-Based Cough Syrup as a Substitute for
Licit and Illicit Drugs: A Theoretical Framework.”Adolescence31 (1996): 239–45.
Einarson, A., D. Lyszkiewicz, and G. Koren. “The Safety of Dextromethorphan in Preg-
nancy: Results of a Controlled Study.”Chest119 (2001): 466–69.