Getting a new job, adopting a child or satisfying a probation officer may require a drug test--usually a urine test. People who don't use illegal drugs will usually test negative. But some prescribed and over-the-counter drugs can yield a false-positive test. These drugs may be antibiotics, painkillers, antidepressants, cold medicines and other medicines.
People who take a drug that could yield a false-positive may be wise to bring it to the test--in the prescription bottle if prescribed--to show the tester for possible notation in the record.
According to Dr. Srinivas B. Rapuri and colleagues in their August 2006 article in "Current Psychiatry" on false-positive urine drug screens, amoxicillin and most antibiotics can yield a false-positive test result for cocaine. They also say antibiotics in the quinolone category can yield a false positive for heroin or morphine.
Patients taking common drugs for depression can yield false-positives for amphetamines, such as bupropion, or Wellbutrin, and fluoxetine, also known by the brand name Prozac, according to Rapuri and colleagues. If subjects actually are taking amphetamines, the drug stays in the urine for up to two days, say Drs. Gifford Lum and Barry Mushlin in their June 2004 article for "Laboratory Medicine." In addition, they say for patients actually taking benzodiazepines, the evidence stays in the urine for up to 21 days.
In a study by Kevin M. Nasky, D.O. and colleagues, reported in the journal "Psychiatry" in 2009, the researchers found 26 patients who tested positive for benzodiazepines were actually false positives for patients taking sertraline, or Zoloft.
According to Karen Moeller and colleagues in a January 2008 article in Mayo Clinic Proceedings, despiramine, or Norpramine, may give a false positive for amphetamine. Moeller also notes imipramine may give a false-positive reading for phencyclidine, a hallucinogenic drug.
Moeller and colleagues say ibuprofen can give a false-positive for pheycyclidine, as may meperidine, also known as Demerol, or ketamine, an anesthetic. In addition, the painkiller tramadol, also known as Ultram, may also give a false-positive reading for phencyclidine. She also notes nonsteroidal anti-inflammatory drugs--NSAIDs--may give false readings for marijuana.
In their 2006 "Journal of Family Practice" article on false positives in urine screening, Dr. E. Chris Vincent and colleagues note that NSAIDs can give false positives for barbiturates.
Moeller says the anti-migraine prescribed drug Midrin may give a false positive reading for amphetamine.
Cold Medicines and Antihistamines
According to Rapuri and colleagues, nasal decongestants and pseudoephedrine, a cold medicine ingredient, can cause false positives for amphetamines on a urinary drug screen. They add that Nyquil, an over-the-counter cold medication, can give a false positive for methadone.
Moeller and colleagues note that promethazine--Phergan--can give a false positive reading for amphetamines in a urine test.
Rapuri and colleagues say drugs such as pantoprazole, or Protonix, a drug in the proton pump inhibitor class used to treat ulcers and acid reflux, can give a false-positive for marijuana. Moeller says all proton pump inhibitors can give a false reading for mraijuana. In addition, rantidine, or Zantac, also an acid reflux drug, can yield a false-positive for amphetamine, says Moeller.
Phentermine, or Adipex, and benzphetamine, also known as Didrex, drugs prescribed to help individuals lose weight, can cause a false-positive for illegal amphetamines, according to Moeller.
Moeller says labetalol--Normadyne--a blood pressure medication, can give a false positive reading for amphetamines.
- "Laboratory Medicine"; Urine Drug Testing: Approaches to Screening and Confirmation Testing; Gifford Lum, M.D. and Barry Mushlin, M.D; June 2004
- "Current Psychiatry"; 'Weed' Out False-Positive Urine Drug Screens; Srinivas B. Rapuri, M.D., et al.; August 2006
- "Mayo Clinic Proceedings"; Urine Drug Screening: Practical Guide for Clinicians; Karen E. Mueller, PharmD, et al.; January 2008
- "Psychiatry"; False-Positive Urine Screening for Benzodiazepines: An Association with Sertraline?; Kevin M. Nasky, D.O., et al. July 2009
- "Journal of Family Practice"; What Common Substances Can Cause False Positives on Urine Screens for Drugs of Abuse?; E. Chris Vincent, M.D., Arthur Zebelman, PhD. and Cheryl Goodwin, MLS; 2006