Q. Can excess intake of water give false negative drug test?

Answered by
Dr. Sumit Srivastava
and medically reviewed by iCliniq medical review team.
Published on Mar 31, 2016

Hi doctor,

I took a drug test and it came out negative, I am on Oxycodone 5 mL, Gabapentin, Methocarbamol and Lisinopril. How could it come out negative while taking these drugs? I drink a lot of water. Is this the cause? How does this happen? Please help.

Dr. Sumit Srivastava

General Medicine Internal Medicine


Welcome to icliniq.com.

  • Two common potential causes for false negative opiate tests are using the wrong test for a specific opiate or having an insufficient concentration of an opiate in the sample.
  • Other possible reasons can be due to dilution for example ingesting a substantial amount of water like you take or you are an ultrafast metabolizer.
  • Urine drug test is widely used for testing for opioids and illicit drugs. There are two types of test, a screening test and a confirmatory test.
  • The screening test uses an immunoassay to look for the parent drug or metabolite. Most screen for Marijuana, Cocaine, Opiates, PCP (Phencyclidine) and Amphetamines, while some also test for Benzodiazepines and Methadone.
  • The confirmatory urine drug test is done by gas chromatography or mass spectrometry (GC/MS) or high-performance liquid chromatography (HPLC). This test is highly specific and is typically used when testing for the presence of a specific drug is needed.
  • The common drugs tested are
  1. Amphetamines.
  2. Barbiturates.
  3. Benzodiazepines.
  4. Cannabinoids (THC - tetrahydrocannabinol, Marijuana).
  5. Clenbuterol.
  6. Cocaine.
  7. Codeine.
  8. Euphorics (Ecstasy).
  9. LSD (Lysergic acid diethylamide)
  10. Methamphetamines.
  11. Nicotine (Cigarettes).
  12. Opiates.
  13. Phencyclidine (PCP).
  14. Phenobarbital.
  15. Steroids.

For further information consult an internal medicine physician online --> https://www.icliniq.com/ask-a-doctor-online/internal-medicine-physician

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