Urine Toxicology Screen

Author: Michelle Lin, MD
Updated: 7/22/2010

Urine Toxicology Screen

Drug Causes False (+) Test Duration of detectability
Amphetamines Amantadine, Buproprion, Chlorpromazine, Desipramine, Fluoxetine, L-methamphetamine in nasal decongestant, Labetalol, Methylphenidate (Ritalin), Phentermine, Phenylephrine, Phenylpropanolamine, Promethazine, Pseudoephedrine, Ranitidine, Thioridazine, Trazodone 2-3 days
Benzodiazepines Oxaprozin, Sertraline 3 days for short acting (e.g. lorazepam) and up to 30 days for long acting (e.g. diazepam)
Cocaine Topical anesthetics which have cocaine 2-3 days (occasional user), up to 8 days (heavy user)
Opiates Dextromethorphan, Diphenhydramine, Fluoroquinolones, Poppy seed, Quinine, Rifampin, Verapamil 1-3 days
Phenycyclidine Dextromethorphan, Diphenhydramine, Ibuprofen, Imipramine, Ketamine, Lamotrigine, Meperidine, Thioridazine, Tramadol, Venlafaxine 7-14 days
Marijuana (tetrahydrocannabinol) Dronabinol, NSAID, Pantoprazole and other proton pump inhibitors 3-5 days with 1x use, 5-7 days with 4x/wk use, 10-15 days with daily use, >30 days with long term and heavy use

Pearl: MDMA (Ecstacy) may not be positive on amphetamine drug screen, unless specifically screen for MDMA.

Benzodiazepines

Benzodiazepines are popular. In the U.S., alprazolam, clonazepam, lorazepam, and diazepam are among the most commonly prescribed medications in the outpatient setting.

Important points on benzodiazepine urine toxicology test:

  1. Most benzodiazepines screens look for oxazepam, because diazepam and chlordiazepoxide both are metabolized to oxazepam.
  2. The test does not specifically look for alprazolam, clonazepam, lorazepam (or many others). Therefore, a negative result does not necessarily rule out use of these agents.
  3. Benzodiazepines vary in reactivity and potency and can trigger a positive result due to cross-reactivity.

Bottom Line

A negative result doesn't rule out benzodiazepine ingestion, and a positive result only guarantees that oxazepam, diazepam, or chlordiazepoxide is present.

Opioid vs Opiate

These two terms are often used interchangeably and really shouldn't be.

  • Opioid: Broad category name which encompasses opiates, semi-synthetic, and synthetic agents
  • Opiate: Refers to only naturally occurring opioids
Opiates Semi-Synthetic Synthetic
Opium Heroin Fentanyl
Morphine Hydrocodone Methadone
Codeine Hydromorphone Tramadol
| Oxycodone
| Oxymorphone
| Buprenorphine
  • Oxycodone, a semi-synthetic, is similar to morphine.
  • Methadone, a synthetic, has a completely unrelated structure.

LEARNING POINTS

  1. Notice the name of the urine drug screen next time you order one. It is opiates (not opioids).
  2. The test was designed to look for heroin (technically a semi-synthetic) via its metabolite, 6-monacetyl morphine. It also picks up morphine and codeine.
  3. The test does not specifically look for oxycodone, hydromorphone, hydrocodone, etc. They can trigger a positive result due to their structural similarities, but not in every case. Therefore, a negative result doesn't rule out use of these common drugs of abuse.
  4. Synthetics will never cross-react with the opiate urine drug screen. They are too structurally dissimilar. That's why there is a separate test for methadone.

Bottom Line

A negative result doesn't rule out opioid ingestion, and a positive result only guarantees that heroin, morphine, or codeine is present.

References

  • Standridge JB, Adams SM, Zotos AP. Urine drug screening: a valuable office procedure. Am Fam Physician. 2010 Mar 1;81(5):635-40. [PubMed]
  • Geraci, M.J., Peele, J., McCoy, S.L. et al. Int J Emerg Med. 2010 Nov 3: 327. doi:10.1007/s12245-010-0235-3