Postmortem Toxicology: What Drug Levels Can—and Cannot—Prove

By Shaun D. Carstairs, MD, DFACMT, FACEP
Board-certified in Emergency Medicine, Medical Toxicology, and Addiction Medicine
Last medically reviewed: November 4, 2026

A postmortem drug concentration is a measurement from a specimen collected after death. It is not, by itself, a direct measurement of the drug concentration at the moment of death, the dose taken, or the cause of death.

Postmortem toxicology can be essential in a medicolegal death investigation. It may document exposure to a drug, quantify that drug in a particular specimen, identify co-exposures, and help determine whether a substance plausibly contributed to death. But the interpretation of a postmortem drug level is more complex than comparing a number with a published “therapeutic,” “toxic,” or “fatal” range.

The significance of a result depends on the drug, the specimen and collection site, the postmortem interval, postmortem redistribution, drug stability, tolerance, co-exposures, medical treatment, autopsy findings, clinical history, and the circumstances surrounding death.

1. What can a postmortem drug result establish?

When an appropriate specimen has been collected and analyzed with a validated method, a postmortem toxicology result can establish that a particular drug or metabolite was detected in that specimen. A quantitative result can establish the measured concentration in that specimen at the time of analysis, subject to the laboratory method and its measurement uncertainty.

Depending on the drug and case circumstances, that information may support conclusions about prior exposure and may contribute to an opinion about toxicity or causation. The toxicology result is strongest when interpreted together with the autopsy, scene investigation, prescription and medication history, medical records, witness information, and other relevant evidence.

2. Why is the postmortem concentration not necessarily the concentration at the time of death?

After death, drug concentrations can change. One important process is postmortem redistribution, in which drugs may move between tissues, organs, and blood after circulation has stopped. Drugs stored at relatively high concentrations in organs or tissues may diffuse into nearby blood or other compartments.

The degree and direction of change vary by drug and by case. Postmortem redistribution is not a single predictable correction that can simply be subtracted from a laboratory value. Studies comparing antemortem and postmortem concentrations show substantial drug-dependent and case-dependent variability.

For this reason, a postmortem blood concentration generally should not be treated as if it were an antemortem serum or plasma level obtained from a living patient at the same point in time.

3. The specimen and collection site matter

Not all postmortem blood samples are equivalent. Peripheral blood, particularly femoral blood collected appropriately, is generally preferred for quantitative interpretation because it is less affected by redistribution from central organs than cardiac or other central blood. Even peripheral blood, however, is not immune from postmortem change.

Other specimens may provide complementary information:

Urine may document prior exposure but usually does not directly reflect the concentration producing pharmacologic effects at death.
Vitreous humor is relatively protected from some postmortem changes and can be useful for selected analytes, although drug-specific reference information may be limited.
Liver, brain, muscle, and other tissues may be useful when blood is unavailable or when tissue distribution is relevant, but tissue concentrations cannot automatically be interpreted using blood reference ranges.
Gastric contents may support recent ingestion in some circumstances but do not, by themselves, establish the absorbed dose.

Attorneys reviewing a toxicology report should identify exactly which specimen was tested, where it was collected, when it was collected, and how it was preserved.

4. “Therapeutic,” “toxic,” and “fatal” ranges are not bright-line thresholds

Reference tables can provide useful context, but they are not automatic rules for deciding causation. Published ranges may be derived from different populations, specimen types, analytical methods, clinical settings, or postmortem case series. Considerable overlap can occur between concentrations reported in people receiving therapeutic treatment, people showing toxicity, and people whose deaths were attributed to the same drug.

Recent forensic research continues to demonstrate substantial overlap in postmortem drug concentrations and emphasizes interpretation within a broader framework that includes pathology, clinical history, co-administered substances, tolerance, and the circumstances of death.

Accordingly, a concentration above a published “fatal” value does not necessarily prove that the drug caused death, and a concentration below such a value does not necessarily exclude a clinically important or fatal drug effect.

5. Tolerance can materially change the meaning of a concentration

Repeated exposure to some drugs can produce pharmacologic tolerance. A concentration associated with profound toxicity in a drug-naive person may have different effects in someone with substantial chronic exposure. This issue is particularly important with opioids and certain sedative drugs.

Useful evidence may include prescription records, prior toxicology results, pain-management records, treatment for substance use disorder, previous overdose encounters, pharmacy data, and other records bearing on chronic use. Tolerance should not be assumed merely because a drug is present, but it should be considered when the history supports it.

6. Multiple drugs may matter more than any single number

Many postmortem cases involve more than one drug. Opioids may be present with alcohol, benzodiazepines, gabapentinoids, sedating antihistamines, antidepressants, stimulants, or other substances. The clinical effect of a combination cannot always be understood by evaluating each drug concentration in isolation.

Some combinations can produce additive or synergistic pharmacologic effects, while other detected substances may be incidental. A sound analysis asks what each substance can plausibly contribute, whether the combination is pharmacologically important, and whether alternative causes of death remain.

7. Can the concentration establish the dose or exact time of ingestion?

Usually not by itself. A postmortem concentration is influenced by absorption, distribution, metabolism, elimination, tolerance, postmortem redistribution, specimen site, and the interval between exposure, death, collection, and analysis.

Likewise, parent-drug-to-metabolite ratios are not universal clocks. In some narrowly defined circumstances, drug-specific pharmacokinetic information may contribute to a timeline, but a simple ratio generally should not be used to assign an exact time of ingestion without a scientifically appropriate foundation.

A postmortem concentration also does not ordinarily permit a reliable backward calculation of the dose taken. Scene evidence, prescription history, pill counts, witness statements, gastric contents, prior concentrations, and other evidence may be relevant, but each has limitations.

8. Medical treatment and resuscitation can affect interpretation

Medications administered by EMS, emergency clinicians, anesthesia teams, or inpatient providers may later appear in postmortem toxicology. The medication administration record therefore matters. Resuscitation, transfusion, intravenous fluids, extracorporeal support, prolonged hospitalization, and organ failure may also alter drug distribution or elimination before death.

When death follows medical treatment rather than occurring at the scene, it is particularly important to reconstruct what drugs were present before treatment, what drugs were administered therapeutically, and how much time elapsed before the postmortem specimen was obtained.

9. Decomposition, storage, and drug stability can change results

Postmortem specimens are not static. Depending on the substance, concentrations may decrease, increase, or become more difficult to interpret because of chemical instability, enzymatic activity, microbial activity, decomposition, storage conditions, or delayed analysis.

This does not make postmortem toxicology unreliable. It means that the condition and handling of the specimen are part of the interpretation. For cases involving a prolonged postmortem interval or advanced decomposition, alternative specimens and drug-specific stability information may become especially important.

10. A negative result does not always exclude exposure

The significance of a negative postmortem toxicology report depends on what the laboratory actually tested for. Screening panels do not include every drug, and emerging substances may require targeted methods. A drug may also be below the laboratory’s reporting limit, may have degraded, or may no longer be detectable in a particular specimen.

Before treating a negative result as proof that a drug was absent, review the laboratory’s scope of testing, analytical method, reporting limits, specimen type, and any relevant drug-specific limitations.

11. Questions attorneys should ask about a postmortem drug level

What specimen was tested? Identify the matrix and, for blood, the collection site.
Was the sample peripheral or central? Determine whether femoral/peripheral blood, cardiac blood, or another source was used.
What analytical method was used? Confirm whether identification and quantitation were performed with an appropriate validated forensic method.
What does the laboratory’s number actually represent? Distinguish the measured concentration from an inferred concentration at the time of death.
Is the drug known to undergo postmortem redistribution or instability? Review drug-specific evidence rather than assuming all substances behave alike.
What reference population is being used? Determine whether comparison ranges come from living therapeutic patients, impaired drivers, overdose survivors, postmortem cases, or another population.
Is tolerance supported by the history? Review prescriptions, prior toxicology, substance-use history, and treatment records when relevant.
What other drugs were present? Consider the entire toxicology profile and potential pharmacodynamic interactions.
Were medications administered before death? Compare EMS and hospital medication records with the toxicology findings.
What competing causes are present? Integrate autopsy findings, medical history, trauma, disease, and other plausible explanations.
What conclusion is actually supported? Separate evidence of exposure from opinions about impairment, toxicity, contribution, cause, and manner of death.

12. Records most useful for a postmortem toxicology review

Complete autopsy report and cause/manner-of-death documentation
Original complete postmortem toxicology report, including specimen source and collection site
Laboratory analytical method, reporting limits, and interpretive comments when available
Specimen collection, preservation, storage, and chain-of-custody information when relevant
Scene investigation, law-enforcement, and witness information concerning possible exposure
EMS, emergency department, hospital, and resuscitation records
Medication administration records
Prescription-monitoring and pharmacy records when legally available and relevant
Prior medical, pain-management, addiction-treatment, and toxicology records bearing on tolerance
Prior or subsequent laboratory testing relevant to the timeline
Information concerning the postmortem interval and degree of decomposition

What a postmortem drug level can—and cannot—prove

A postmortem concentration can help establish:

That a drug or metabolite was detected in the tested specimen
The measured concentration in that particular specimen
Whether the finding is consistent or inconsistent with particular toxicologic scenarios when interpreted with other evidence
Whether the drug is a plausible contributor to toxicity or death when the full case record supports that conclusion

A postmortem concentration generally cannot, by itself, establish:

The exact drug concentration in circulating blood at the moment of death
The exact dose taken
The precise time of ingestion or administration
The degree of impairment immediately before death
Whether the decedent was tolerant to the drug
That a detected drug was the sole cause of death
Cause or manner of death without integration of the broader medicolegal investigation

When medical toxicology review can help

A medical toxicology review can help determine whether the toxicology findings are being interpreted within an appropriate pharmacologic, clinical, and postmortem framework. The analysis may include specimen selection, postmortem redistribution, drug stability, tolerance, co-exposures, medical treatment, competing causes, and the strength of the proposed causal inference.

Shaun D. Carstairs, MD, DFACMT, FACEP is board-certified in Medical Toxicology, Addiction Medicine, and Emergency Medicine and can assess matters that cross those clinical boundaries when the requested assignment fits his expertise.

Selected References

Algahtani T, Rock KL, Rice-Davies K, et al. Population-Stratified Distributions of Post-Mortem Blood Drug Concentrations: An Epidemiological Framework for Contextual Interpretation. Drug Test Anal. 2026. doi:10.1002/dta.70163.
Truver MT, Chronister CW, Davis GG, et al. Application of professional best practices in postmortem forensic toxicology. J Anal Toxicol. 2025;49(8):529-541. doi:10.1093/jat/bkaf061.
Stephenson L, Van Den Heuvel C, Scott T, Byard RW. Difficulties associated with the interpretation of postmortem toxicology. J Anal Toxicol. 2024;48(6):405-412. doi:10.1093/jat/bkae052.
Abdelaal GMM, Hegazy NI, Etewa RL, Elmesallamy GEA. Postmortem redistribution of drugs: a literature review. Forensic Sci Med Pathol. 2024;20(4):1483-1490. doi:10.1007/s12024-023-00709-z.
Mantinieks D, Gerostamoulos D, Glowacki L, et al. Postmortem Drug Redistribution: A Compilation of Postmortem/Antemortem Drug Concentration Ratios. J Anal Toxicol. 2021;45(4):368-377. doi:10.1093/jat/bkaa107.
AAFS Standards Board. ANSI/ASB Best Practice Recommendation 156: Best Practices for Specimen Collection and Preservation for Forensic Toxicology. First Edition. 2023.

These references address general principles of postmortem toxicology, specimen selection, postmortem redistribution, and interpretation of drug concentrations. A case-specific review may require drug-specific literature, laboratory documentation, and additional forensic pathology or toxicology evidence.

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This resource is intended for general educational purposes for attorneys and does not constitute patient-specific medical advice, legal advice, or a case opinion.