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, DABAT, FAACT, FASHP

Bryan D. Hayes, PharmD, DABAT, FAACT, FASHP

Leadership Team, ALiEM
Creator and Lead Editor, Capsules and EM Pharm Pearls Series
Attending Pharmacist, EM and Toxicology, MGH
Associate Professor of EM, Division of Medical Toxicology, Harvard Medical School
Bryan D. Hayes, PharmD, DABAT, FAACT, FASHP


EM Pharmacist & Toxicologist @MassGeneralEM | Asst Prof @HarvardMed/@EMRES_MGHBWH | @ALiEMteam leadership | Capsules creator, ALiEMU | President, ABAT | #FOAMed