We have heard speculation that DXM may cause false positives for both PCP and Opiates in standard urine tests. After doing a bit of research on the web we found a small handful of references on the topic. Most of these support the possibility that DXM may cause false positives,
but the only peer reviewed journal article refutes that normal doses of DXM cause false positives for Opiates.
Erowid has received one report of an individual who tested positive for PCP a few hours after ingesting DXM.(1) Another report was posted to usenet where
an individual purchased and ingested a medium-high dose DXM powder. He ended up in the emergency room where he tested positive for both PCP and Opiates. His conclusion was that the
DXM powder he had purchased was not pure, but there is every reason to believe that it may have been pure DXM which caused both of these false positives.(2)
The one peer reviewed study which we found tested normal label recommended cough suppressant doses of DXM. They tested twenty individuals after either 20 or 40 mg doses of DXM and found that
none tested positive for Opiates 72 hours later (using EMIT).(3) Obviously this is a significantly lower dose than most recreational users choose. The primary thing this tells us is that it might be difficult to use medicinal DXM use as an excuse for testing positive for Opiates.
Erowid DXM Vault : Drug Testing