What Can Cause a False Positive for PCP

PCP is an abbreviation referring to an illicit drug named Phencyclidine, which is similar to Ketamine. Because of PCP’s effectiveness on certain receptors in the brain, PCP is still illegally marketed; although it was previously banned and withdrawn.

PCP is abused for achieving recreational purposes, as its administration results in delirium, hallucinations, confusion and psychosis-like symptoms. That’s why drug tests crucially test for PCP.

What Drugs Can Cause a False Positive

  • Ketamine-containing drugs, such as Ketalar
  • Meperidine –containing drugs, such as Demerol
  • Mesoridazine-containing drugs, such as Serentil
  • Tramadol-containing drugs, such as ConZip and Ultram
  • Venlafaxine-containing drugs, such as Effexor
  • Thioridazine- containing drugs, such as Thorazine
  • Doxylamine-containing drugs, such as Unisom
  • Imipramine-containing anti-depressant, such as Tofranil.

Dextromethorphan-containing drugs, such as a cough and cold drugs, can cause a PCP false positive. For example, Robitussin CoughGels, Delsym, Buckleys Mixture, Creomulsion, Creo-Terpin, DayQuil Cough, Elixsure Cough, Robafen Cough Liquidgels, Scot-Tussin Diabetic, Silphen DM, Sucrets DM Cough, Theraflu Thin Strips Cough, and Triaminic Long Acting Cough

Certain analgesics are known as Non-steroidal anti-inflammatory drugs (NSAIDs), including Ibuprofen, Naproxen, and Tolmetin. Here is a list showing the common examples of drugs containing those analgesics:

Ibuprofen-containing drugs

  • Genpril
  • Motrin IB
  • Advil
  • Midol IB
  • Proprinal.

Naproxen-containing analgesics

  • Aleve
  • EC-Naprosyn
  • Flanax
  • Midol

Tolmetin-containing analgesics

  • Tolectin 600
  • Tolectin
  • Tolectin DS

A group of antibiotics known as Quinolones, such as Ofloxacin, Gatifloxacin. Examples of quinolones-containing drugs, including Maxaquin, Floxin, Noroxin, Norfloxacin,

Tequin, Cipro I.V., Ciprofloxacin, Avelox, Moxifloxacin, Avelox I.V., Baxdela, Trovan and Zagam.

Diphenhydramine-containing drugs, such as Allergy Relief, Allermax, Banophen, Benadryl, Compoz Nighttime Sleep Aid, Diphedryl, Diphenhist, Dytuss, Nytol QuickCaps, Q-Dryl, Quenalin, Scot-Tussin Allergy Relief Formula, Simply Sleep, Sleepinal, Sominex, Tranquil, Twilite, Unisom Sleepgels Maximum Strength, Valu-Dryl, Vanamine PD, Z-Sleep and ZzzQuil.

Why Do Those Drugs Cause A False Positive

The majority of drug tests detect PCP in the system through certain types of assays, which sometimes are not able to specifically detect PCP itself. Instead, those tests work, depending on a structure-based technique that detects not only PCPs-containing drugs; but also all drugs having structures similar to those of PCP and PCP’s metabolites, causing a false positive.

How Long Can Those Drugs Cause A False Positive

As long as those drugs or their metabolites are still in your system, they are likely to cause a PCP false positive.

Importantly, other factors can significantly affect the false positive results of PCP’s tests. Those factors differ from a person to another, including:

  • Your age
  • Your body mass
  • The administered dosage. For example, an overdose of any of the previously-mentioned drugs undoubtedly takes a longer time to be cleared from the body.
  • Whether you’re a light or a chronic user of the previous drugs.
  • Your metabolic rate of drugs, which determines how quickly your body can get rid of those drugs.
  • The type of tests you are required to undergo, as well as the time the test is performed. Each test has a certain time frame to detect certain drugs.



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