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Pharmacy and Medications

Over-the-Counter Drug Presence in Blood and Urine



Can Centrum vitamins, Activated Charcoal, iron vitamins, Bentonite, Equate Fiber Therapy or Milk Thistle effect/show up in a blood or Urine screening?

These are commonly taken by testing subjects before they screen for medical research studies to detox and replentish their blood.

Thank You-


Screening of the blood and urine is useful when searching for drugs of abuse. Most toxic screenings search the urine for 5 abused drugs. These 5 substances include opiates, PCP, cocaine, marijuana, and amphetamines. False positive tests are rare with an occurrence of approximately 1 - 2.5%. Centrum, charcoal, iron, bentonite, fiber, and milk thistle should not show up on a routine drug screening.

It is recommended that any and all positive screenings be followed up by a second, more selective test to confirm the result and rule out any false positives. Although the herbal products mentioned here are not common culprits of producing false positives, there are some consistent over-the-counter medications that may lead to erroneous results. Some common medications include Vicks inhaler, Naproxen, and Dextromethorphan.

Submitted by: Scott Valentine, PharmD Candidate The Ohio State University College of Pharmacy


Any vitamin or fiber therapy product ingested is also metabolized and used by the body in the same way that vitamin-containing food would be. These substances do not typically alter laboratory testing of blood or urine during screening.

Activated charcoal and bentonite are both binding agents that may interfere with absorption of substances in the intestines. These binders do not get absorbed by the body so they will not affect blood or urine screening either.

Milk Thistle is believed to have protective effects on the liver and improve its function. There have been no conclusive clinical trials to prove this effect on the liver, and most studies have mixed results. Its mechanism of action is mainly thought to be due to an antioxidant effect. This substance will also not have an effect or show up on a blood or urine screening.

Submitted by Eric Waginer, PharmD candidate, University of Cincinnati

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Response by:

Jill RK Griffith, RPh, PharmD, CSPI
Clinical Assistant Professor
College of Pharmacy
University of Cincinnati

Jan Scaglione, MT, PharmD, D.ABAT
Assistant Professor of Pharmacy Practice
College of Medicine
University of Cincinnati