Phencyclidine

Some medications can cause false‑positive PCP (phencyclidine) immunoassay results: dextromethorphan (cough syrups), ketamine, tramadol, diphenhydramine and dextropropoxyphene. Rare reports exist for certain antidepressants and antipsychotics. Confirmatory testing (GC‑MS or LC‑MS/MS) distinguishes true PCP from cross‑reacting drugs. If you test positive, request confirmatory testing and bring a full medication list.

Phencyclidine (PCP) is a dissociative anesthetic that primarily acts as a noncompetitive antagonist at NMDA glutamate receptors, blocking the receptor-associated ion channel and reducing excitatory glutamatergic transmission. It also alters monoaminergic signaling (increasing dopamine and norepinephrine) and interacts with nicotinic, opioid, and sigma receptors, producing analgesia, dissociation, hallucinations, sympathetic stimulation, and psychotomimetic effects.

"Angel dust" is a street name for phencyclidine (PCP), a dissociative anesthetic and hallucinogen originally developed for surgery but discontinued due to severe side effects. It produces detachment, hallucinations, confusion, agitation, violence, numbness, slurred speech, increased heart rate and blood pressure, seizures and coma. Repeated use can cause addiction, memory and cognitive deficits, depression and persistent psychosis.

"Purple Rain" refers to illicit pills or mixtures sold under that name that often contain high‑potency synthetic opioids (like fentanyl) and sedatives (benzodiazepines). They are unpredictable and greatly increase risk of severe sedation, respiratory depression, coma and death. Overdose requires urgent emergency care; naloxone can reverse opioid effects but may not counter sedatives, and multiple doses or supportive breathing may be needed.

Urine immunoassay screens for amphetamines are among the most frequent false positives. Over‑the‑counter decongestants (pseudoephedrine), certain antidepressants (bupropion), some antihypertensives and antihistamines can cross‑react. Opioid screens can also be falsely positive after poppy‑seed ingestion. Immunoassays are prone to cross‑reactivity; confirmatory testing by GC‑MS or LC‑MS/MS is needed to verify a true positive.

Yes. PCP (phencyclidine) increases dopamine levels indirectly. By blocking NMDA glutamate receptors—particularly on inhibitory GABA interneurons—it disinhibits dopaminergic neurons, leading to increased dopamine release and higher synaptic levels. PCP is not a classical dopamine releaser like amphetamines, but this dopaminergic effect contributes to its psychotic, rewarding, and addictive effects.