Peeing into the wind? Urine drug screens, part 2 (opiates)

Peeing into the wind? Urine drug screens, part 2 (opiates)

Apart from benzodiazepines, the opiate urine drug screens (UDS) are probably the most frequently utilized and misunderstood.


For a brief history of the UDS and a review of the test for benzodiazepines, check out part 1 of our two-part series.


To properly interpret the UDS for opiates.

First, a couple of prerequisites… 

1) Opiate vs. Opioid

  • These two terms are often used interchangeably and really shouldn’t be.
  • Think of it like this: ‘Opioid’ is the broad category name while ‘opiate’ simply refers to the naturally occurring opioids. The term ‘opioid’ encompasses opiates, semi-synthetic, and synthetic agents. The chart below gives a few examples of each.

2) Forgive me in advance for the structures, but I think it’s important to understand why a drug may or may not show up on the UDS. I can’t get rid of the chemist in me… 

Opioid structures
  • The point here isn’t to analyze structures, but simply to see the similarities between morphine, heroin, and oxycodone.
  • Oxycodone, a semi-synthetic, is similar to morphine.
  • Methadone, a synthetic, has a completely unrelated structure.


  1. Notice the name of the UDS 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 UDS. They are too structurally dissimilar. That’s why we have a separate test for methadone.


A negative result doesn’t rule out opioid ingestion and a positive result only guarantees that heroin, morphine, or codeine is present. Like the benzo screen… not very helpful, in my humble opinion.


Bryan D. Hayes, PharmD, FAACT, FASHP

Bryan D. Hayes, PharmD, FAACT, FASHP

Chief Science Officer, ALiEM
Creator and Lead Editor, Capsules series, ALiEMU
Attending Pharmacist, EM and Toxicology, MGH
Assistant Professor of EM, Harvard Medical School
  • SF Tox

    The last time our chemistry lab looked at this, in general the commercial UDS products they knew of had generally 20-30% cross-reactivity with hydromorphone and hydrocodone and generally 0% cross-reactivity with oxycodone.

  • Anonymous

    There are specific oxycodone/oxymorphone Point of Care and lab based ELISA tests that have resonable sentitivity if you have acsess we still dont.

    Else have to go GC-MS which is hardly point of care or rapid turn around.

  • Hassan Almaateeq

    One time i received one obtunded pt who waked up after naloxone 0.8 mg and hit me on chest 🙁
    Drug screen came negative for opioids 🙂

    What about pethidine ? Which class it is & does it show on urine screen?

    • Bryan D. Hayes

      Dear Hassan. Thanks for your question. Pethidine is another name for meperidine. It is a synthetic opioid and would not be expected to show up on the typical urine toxicology screen.

  • Something I stress to my residents frequently. I have yet to make a clinical decision based on UDS. Sure, I’ve made some social ones. You tested positive for cocaine? No drugs of abuse for you. Treat the patient, not the markedly flawed test. Besides, the treatment for nearly anything you do get is “supportive care”, which you should already be doing.
    (Yes, there are forensic reasons to test for drugs, but those are typically beyond the scope of the ED.)

  • wondering

    what about bupe/subs?