By: Allison Muller Pharm.D, D.ABAT, FAACT

The Difference Between Opiates and Opioids

Opiates are naturally occurring compounds derived from the opium poppy plant, namely morphine and codeine. Opioids are artificial and are either fully synthetic (e.g., fentanyl) or semi-synthetic drugs (e.g., heroin, oxycodone, hydrocodone). Both opioids and opiates attach to opioid receptors, which are nerve cells in the brain, spinal cord, and other organs. These receptors exist in the body because we have endogenous opioids (“feel good” hormones such as endorphins), not because it was anticipated that opiates or opioids would one day be used. When opioids or opiates interact with opioid receptors, effects such as pain relief, mood changes, drowsiness, slower breathing, decreased movement in the gastrointestinal tract, nausea, vomiting, and constricted pupils can result.

Since opiates and opioids do the same thing in the body and are generally used for the same purposes, the terms are often used interchangeably. This does not present a problem except in deciphering the results of a drug screen. This is because opiates and opioids are compounds from different drug families. For example, a drug screen looking for opiates is not going to pick up oxycodone. Why? Because oxycodone is an opioid, not an opiate. There are some exceptions, as there can sometimes be a crossover between drug families, or in the case of heroin (an opioid), it metabolizes (breaks down) into morphine (an opiate).

Opioids are “downers”. That is, they suppress the central nervous system. This results not only in changes in alertness ranging from drowsiness to loss of consciousness but also changes in respiration (breathing). It is the depression of the respiratory center in the brain that leads to opioid fatalities, which have increased more than eight times since 1999.1 In cases involving drug screening, an opioid toxicology expert witness may be needed to review the drug screen and determine the presence of opioids and/or opiates.  Such cases where an opioid toxicology expert witness may be used include criminal matters, personal injury lawsuits, employment law cases, and even family law matters.

Opioid Levels and Drug Screens

When levels of opioids (or opiates) are measured, there are challenges with interpreting what these levels (blood, urine, antemortem, postmortem) mean. Attorneys (and toxicologists) want to know: what story do these levels tell us? Interpretation can often be challenging because factors such as tolerance, the presence of other drugs in the patient’s system (e.g., benzodiazepines such as diazepam or lorazepam), and the source of testing (more relevant in postmortem toxicology testing) are all important to consider. So, it’s not as simple as finding a reference that provides “toxic” or “fatal” levels and automatically attributing it to the person’s symptoms or fatal demise. An opioid toxicology expert witness is often used to offer opinions on the meaning of a drug test result in a particular case.

The Use of Naloxone

In response to the opioid crisis, now worsened by the COVID-19 pandemic and the increase of fentanyl in illicit drug supplies, the public is being educated about the use of naloxone (also known as Narcan®). This drug is still a prescription product. However, most states have a standing order that allows it to be purchased without a prescription from a healthcare provider. Also, steps are being taken to make naloxone over-the-counter. Although naloxone can save lives in the face of opioid toxicity, timing is everything with this antidote. Naloxone does not work 100% of the time. This antidote may not have been given early enough in the downward spiral of the opioid-poisoned patient’s clinical course; the dose was not high enough, or a combination of the two. An opioid toxicology expert witness may be asked to determine if naloxone would have likely been effective had it been given at a different time or if failure of naloxone to restore breathing and consciousness rules out opioid toxicity. 


There is a time and a place for the therapeutic use of opioids. However, the safe dose for a specific patient can be more of an art than a science. This is because patients are not one-dimensional. As previously stated regarding the interpretation of opioid or opiate levels, patient-specific factors will dictate who has an adverse event or fatality with opioid therapy or illicit opioid use. An opioid toxicology expert witness may be needed to determine whether and how these factors contributed to an overdose or other adverse event.

About Allison Muller Pharm.D, D.ABAT, FAACT 

opioid toxicology expert witness

Dr. Muller is a board-certified toxicologist and a Fellow of the American Academy of Clinical Toxicology. She is also a registered pharmacist with over 20 years’ experience in the field of clinical toxicology. She spent two decades as a clinical toxicologist and managing director at the Poison Control Center at The Children’s Hospital of Philadelphia, consulting on toxicology cases from 21 counties in Pennsylvania and Delaware. Her expert witness experience has involved cases related to alcohol, drugs of abuse (i.e., opioids, marijuana, synthetic cannabinoids, cocaine), carbon monoxide, medication errors, and postmortem toxicology. She can be contacted at (215) 593-5805 (m) or


  1. The drug overdose epidemic: behind the numbers. Accessed December 15, 2022.