A postmortem toxicology report identifies the drugs, alcohol, poisons, gases, and other chemicals present in a deceased person’s body, along with how much of each substance was detected. The report draws on laboratory analysis of blood, urine, organ tissue, and sometimes less obvious specimens like the fluid inside the eye or even hair and nails. But the numbers on the report are not as straightforward as they sound, because death itself changes drug concentrations in ways that make interpretation far more complicated than a simple blood test on a living patient.
What Specimens Get Collected
During an autopsy, a forensic pathologist collects multiple types of biological samples for the toxicology lab. The most important are blood from the femoral vein (in the thigh), urine, vitreous humor (the gel-like fluid from the eye), stomach contents, and organ tissue from the liver and lungs.1Oxford University Press. Guidelines for Collection of Biological Samples for Clinical and Forensic Toxicological Analysis Depending on the circumstances, other materials may be taken too: cerebrospinal fluid, bile, brain tissue, bone marrow, or skeletal muscle. The reason for collecting so many different samples is that no single specimen tells the full story. Each one reflects drug levels differently, and comparing concentrations across multiple sites helps the toxicologist piece together what actually happened.
Femoral blood is the gold standard because it sits relatively far from the major organs of the chest and abdomen, which makes it less vulnerable to a phenomenon called postmortem redistribution (more on that shortly).2PubMed. Postmortem drug redistribution–human cases related to results in experimental animals Cardiac blood is also collected, but drug concentrations in heart blood tend to run higher than peripheral blood because drugs leach out of nearby organs like the lungs and liver after death. Urine, when present, is useful because it reflects what the kidneys had already filtered before death, giving a window into what substances the person used in the hours or days beforehand.
What the Lab Actually Tests For
The testing process typically starts with broad screening panels designed to flag the presence of common drug classes: opioids, benzodiazepines, amphetamines, cannabis, cocaine and its metabolites, barbiturates, and antidepressants. Early screening often uses immunoassay techniques, which are fast but imperfect. A study comparing immunoassay with a more advanced mass spectrometry method found that immunoassay produced a meaningful number of both false positives and false negatives, largely because of higher cutoff thresholds and interference from the biological matrix of postmortem specimens.3PubMed. Comparison between drug screening by immunoassay and ultra-high performance liquid chromatography/high-resolution time-of-flight mass spectrometry in post-mortem urine For that reason, positive screening results are confirmed with more precise instruments, and many labs now run advanced mass spectrometry methods that can identify hundreds of individual compounds in a single analysis.
Beyond prescription and recreational drugs, the lab checks for alcohol (ethanol), carbon monoxide, cyanide, heavy metals like mercury and cadmium, and volatile chemicals like solvents or inhalants. If a specific poison is suspected based on the circumstances of death, additional targeted tests are ordered. The scope of testing depends partly on what the medical examiner or coroner already knows about the case: a suspected heroin overdose and a suspicious household death will prompt very different panels.
Why Drug Levels After Death Don’t Mean What They’d Mean in a Living Person
One of the trickiest parts of postmortem toxicology is that drug concentrations measured in a dead body do not correspond neatly to clinical blood levels in living patients. A review of published reference ranges found wide gaps between therapeutic serum concentrations used in clinical medicine and postmortem blood concentrations. For roughly a third of the drugs examined, the upper limit of the postmortem range was more than three times the upper limit of the therapeutic range.4PubMed. Postmortem drug concentration intervals for the non-intoxicated state – A review This means that seeing a drug level that looks alarmingly high on paper does not automatically mean the person was poisoned or overdosed. Conversely, a level that looks “normal” might not have been normal for that individual.
Separate research has confirmed that therapeutic plasma concentrations are of limited value when interpreting postmortem femoral blood results, and that postmortem-specific reference data should be used instead.5PubMed Central. Drug concentrations in post-mortem femoral blood compared with therapeutic concentrations in plasma The upshot for families waiting on a toxicology report is that the numbers alone don’t tell you the cause of death. A forensic toxicologist interprets those numbers in context, considering the person’s medical history, the circumstances surrounding the death, the autopsy findings, and the pattern of drugs across different specimens.
Postmortem Redistribution Changes the Numbers
After death, drugs don’t stay put. They move from organs with high concentrations into surrounding blood and tissue through passive diffusion, a process called postmortem redistribution. The lungs, liver, and heart are drug-rich reservoirs, and substances stored in those organs gradually seep into nearby blood vessels. This is why cardiac blood often shows inflated drug levels compared to blood drawn from the femoral vein in the leg.6PubMed Central. Postmortem redistribution of drugs: a literature review
A Swedish study that compared drug concentrations across six different blood sampling sites in autopsy cases found that right heart blood levels averaged about 1.3 times the levels in the iliac vein (a peripheral site). Drugs that distribute widely through the body during life showed even larger differences between central and peripheral sites. Time since death mattered too: when the interval was long, arterial blood concentrations ran about twice as high as venous blood from the same region.7PubMed. Postmortem blood sampling-Comparison of drug concentrations at different sample sites The takeaway from this research is that blood collected sooner after death and from a peripheral vein gives the most reliable picture of what the person’s blood level was around the time they died.
Toxicologists use various markers and ratios to gauge how much redistribution has occurred. Comparing central blood to peripheral blood concentrations, or liver tissue to peripheral blood, helps them estimate whether a measured drug level is trustworthy or artificially elevated.6PubMed Central. Postmortem redistribution of drugs: a literature review None of these markers are perfect, but they give the toxicologist a sense of how cautiously to treat the raw numbers.
Vitreous Humor as a Protected Specimen
The fluid inside the eye turns out to be remarkably useful in postmortem work. Vitreous humor sits in an anatomically isolated compartment, which means it is far less affected by postmortem redistribution than blood is. It contains relatively few compounds that interfere with laboratory analysis, and its chemical makeup stays stable for a longer period after death.8PubMed Central. Vitreous humor analysis for the detection of xenobiotics in forensic toxicology: a review
Vitreous fluid is also analyzed for electrolytes like potassium, sodium, and chloride, and for glucose. These biochemical markers help estimate how long someone has been dead and can flag conditions like diabetic crisis.9PubMed Central. A Rapid Method for Postmortem Vitreous Chemistry-Deadside Analysis For drug screening specifically, vitreous humor picks up fewer metabolites than urine does, but it successfully identifies a wide range of parent compounds, making it a solid backup when blood or urine is unavailable or compromised.10Journal of Analytical Toxicology. Vitreous Humor as an Alternative Matrix for Comprehensive Drug Screening in Postmortem Toxicology by Liquid Chromatography-Time-of-Flight Mass Spectrometry
Alcohol Is Especially Hard to Interpret
Ethanol is one of the most commonly detected substances in postmortem toxicology, but it’s also one of the hardest to interpret. The problem is that bacteria and yeast in a decomposing body can produce alcohol on their own. A person who never had a drink in the days before death can still test positive for ethanol if microbial activity has been active long enough. Higher alcohols, including 1-propanol and isobutanol, often show up alongside microbially produced ethanol and serve as markers that fermentation rather than drinking is the source.11PubMed Central. Modeling Postmortem Ethanol Production/Insights into the Origin of Higher Alcohols
Reliably separating alcohol consumed before death from alcohol produced after death requires a multi-marker approach, combining ethanol levels across different specimens with measurements of metabolites like ethyl glucuronide and ethyl sulfate.12Forensic Science International. Postmortem correlation of ethanol and minor metabolites ethylglucuronide and ethylsulfate in blood, vitreous humor and bile Vitreous humor is especially valued here because its isolated location makes it less susceptible to microbial contamination than blood. Choosing the right specimen and storing it properly is critical for getting a meaningful alcohol result, particularly in bodies that have been dead for more than a day or two.13PubMed. Biological matrices for determining the origin of post-mortem ethanol: Recommendations for collection and storage
What the Ratio Between a Drug and Its Metabolite Can Reveal
When your body processes a drug, enzymes break it down into metabolites. The ratio between the parent drug and its metabolites at the time of death can help toxicologists figure out whether a person took a single massive dose (acute overdose) or had been taking the drug regularly over time. In acute overdoses, the parent drug tends to be present in high amounts relative to the metabolite because the body hasn’t had time to break it all down. In chronic users, the metabolite levels are typically higher because the body has been processing the drug continuously.
This principle was demonstrated in a study of tricyclic antidepressant deaths, where the parent-drug-to-metabolite ratio in liver tissue was dramatically different in overdose cases compared to cases involving therapeutic use.14PubMed. Postmortem tricyclic antidepressant concentrations: assessing cause of death using parent drug to metabolite ratio However, these ratios aren’t always straightforward to read. Postmortem redistribution can alter the ratio for specific drugs in unpredictable ways. A person with a genetic variation that makes them metabolize certain drugs poorly could show a low metabolite ratio even at therapeutic doses. And drug interactions can slow or speed up metabolism in ways that muddle the picture.15PubMed Central. Difficulties associated with the interpretation of postmortem toxicology
Carbon Monoxide and Other Gases
Not everything a toxicology report detects is a pill or a powder. Carbon monoxide poisoning is identified by measuring carboxyhemoglobin, the percentage of hemoglobin in the blood that has bound to carbon monoxide instead of oxygen. Levels above about 5% are flagged as potentially significant, and labs use both spectrophotometric methods and gas chromatography to measure it.16Journal of Analytical Toxicology. Comparative Evaluation of Carboxyhemoglobin Quantification in Postmortem Whole Blood by CO-Oximetry and Headspace Gas Chromatography with Flame Ionization Detection and Atom Absorption Spectrophotometry This matters in fire deaths, furnace malfunctions, and suicides involving vehicle exhaust or charcoal burning.
Measuring carboxyhemoglobin in postmortem blood has its own complications. Decomposition can elevate methemoglobin, a form of hemoglobin that doesn’t bind carbon monoxide. If the analytical method doesn’t account for methemoglobin, it can report falsely high carboxyhemoglobin values. One laboratory found errors exceeding 50% with a standard gas chromatography method that failed to correct for methemoglobin, and developed a modified procedure using a reducing agent to eliminate the error.17Journal of Analytical Toxicology. An Accurate Method for the Determination of Carboxyhemoglobin in Postmortem Blood Using GC-TCD When blood is unavailable or too degraded, thoracic cavity fluid has been shown to correlate strongly with blood carboxyhemoglobin levels and can serve as an alternative specimen.18PubMed. Thoracic cavity fluid as an alternative specimen for carboxyhaemoglobin measurement in post-mortem toxicology
Heavy Metals and Poisons
Toxicology reports can also reveal poisoning by heavy metals like mercury, cadmium, arsenic, and lead. These analyses are usually targeted rather than routine: a lab runs them when the circumstances suggest exposure, such as an unexplained death with symptoms consistent with heavy metal toxicity, or a suspected homicide. Postmortem tissue concentrations of metals like cadmium vary widely by organ, with kidneys typically showing the highest levels, followed by liver and intestine.19PubMed Central. Trace Elements in Post-Mortem Tissues: A Review of Current Evidence and Forensic Challenges Reference values for what constitutes a “normal” postmortem level versus a toxic one are still being refined, which makes interpretation challenging. For mercury specifically, newer analytical methods have proven faster and more reliable than older techniques, improving forensic labs’ ability to confirm mercury poisoning.19PubMed Central. Trace Elements in Post-Mortem Tissues: A Review of Current Evidence and Forensic Challenges
Opioids and the Question of Tolerance
Opioid deaths present a particular interpretive challenge because the difference between a therapeutic dose and a lethal dose depends heavily on the individual’s tolerance. A blood morphine level that would be fatal to someone who never takes opioids might be unremarkable in a person with chronic pain who has been on high-dose opioids for years. This means the toxicologist needs to know, or at least estimate, the deceased person’s prior drug use history before calling an opioid level “toxic.”20PubMed. A review of possible biomarkers for opioid tolerance Researchers have been looking for biological markers that could objectively indicate whether a person had developed opioid tolerance, which would make death investigations less reliant on incomplete medical records and witness accounts.
The role of genetics adds another layer. Variations in the gene for an enzyme called CYP2D6 affect how quickly a person metabolizes certain opioids. Someone who carries specific genetic variants may break down oxycodone much more slowly, leading to higher blood levels at a standard dose. A study that genotyped oxycodone fatality cases found that identifying CYP2D6 variants provided a more definitive explanation for the toxicity in several cases where the drug levels alone were ambiguous.21PubMed. Pharmacogenomics as molecular autopsy for postmortem forensic toxicology: genotyping cytochrome P450 2D6 for oxycodone cases This kind of genetic testing is not yet routine in every forensic lab, but it represents a growing area of postmortem investigation.
When Decomposition Complicates Everything
Bodies that are badly decomposed pose serious problems for toxicology. Bacteria break down some drugs entirely, making them undetectable even though the person took them before death. Other drugs are chemically altered by decomposition products in ways that confuse the analytical instruments. Putrefactive compounds extracted alongside drugs can mask signals or produce false readings, depending on the detection method used.22PubMed. The influence of putrefaction and sample storage on post-mortem toxicology results The result is that a toxicology report from a badly decomposed body often carries wide uncertainty.
This is where alternative specimens become invaluable. Hair and nails are keratinized tissues that trap drugs and their metabolites as they grow. Because they resist decomposition far better than blood or soft tissue, they can reveal a person’s drug use history even when the body is severely degraded. A case report demonstrated that clozapine was detectable in both hair and nails from a decomposed body, confirming the deceased’s long-term medication use when conventional specimens were no longer viable.23PubMed. Determination of clozapine in hair and nail: the role of keratinous biological materials in the identification of a bloated cadaver case Nail analysis in particular allows retrospective investigation of chronic drug exposure over weeks or months.24Current Pharmaceutical Design. Nails in Forensic Toxicology: An Update
In extreme decomposition cases, even insects that have fed on the body can be tested for drugs and toxins. The field of entomotoxicology analyzes larvae and other insects recovered from remains to detect substances the deceased was exposed to before death.25PubMed Central. Toxicological Analysis of Insects on the Corpse: A Valuable Source of Information in Forensic Investigations The concentrations found in insects aren’t directly comparable to blood levels, but they can confirm that a drug was present in the body, which is sometimes the only evidence available.
How the Report Feeds Into Determining Cause and Manner of Death
A toxicology report by itself does not declare a cause of death. The medical examiner or coroner integrates the toxicology results with everything else known about the case: the scene investigation, the person’s medical history, the gross and microscopic findings from the autopsy, and the pattern of substances across different specimens. The toxicology report might show that a lethal combination of fentanyl and benzodiazepines was present, but the medical examiner still has to weigh whether those levels are consistent with lethality given the individual’s tolerance, body weight, and any underlying health conditions.26PubMed Central. Postmortem forensic toxicology
Distinguishing accident from suicide, or therapeutic misadventure from intentional overdose, often depends on details that the numbers alone cannot resolve. Whether the drug was injected, swallowed, or inhaled; whether the dose pattern suggests chronic use or a single acute ingestion; and whether the drug levels are consistent with the behavior witnesses described in the person’s final hours are all factored in. The toxicology report provides critical evidence, but it is one piece of a larger puzzle.
Embalming Artifacts
When a body has been embalmed before an autopsy is ordered, the toxicology results can be contaminated in ways that look like poisoning. Embalming fluids typically contain formaldehyde, methanol, sodium borate, and other chemicals that mix with the body’s fluids and tissues. Vitreous humor that turns pink is a telltale sign that embalming fluid has reached the eyes. In one reported case, methanol was detected in a subdural blood clot from an embalmed 87-year-old woman. The finding initially raised questions about methanol poisoning, but further investigation showed the methanol came from the embalming fluid, not from anything the woman consumed.27PubMed. Methanol Detected in a Subdural Hematoma as an Embalming Artifact Labs experienced in postmortem work know to flag results from embalmed bodies and interpret them with extra caution, but it remains a real source of confusion, especially in cases where the death is reported to the coroner’s office only after funeral preparations have begun.
Why Reports Take So Long
Families waiting for a toxicology report are often told it will take weeks or even months. This timeline frustrates people, but there are practical reasons for it. Comprehensive drug screening requires multiple analytical steps: initial immunoassay screening, confirmatory testing by mass spectrometry, quantification of identified substances, and sometimes additional specialized tests for metals, gases, or unusual poisons. Each step takes time, and forensic laboratories typically handle a heavy caseload with limited staff. Specimens may also need to be sent to reference laboratories for specialized analyses that the local lab cannot perform. The toxicologist’s interpretive report, which contextualizes the raw numbers, adds additional time. In complex cases involving multiple drugs or unusual circumstances, the interpretation itself requires careful review of the scientific literature and consultation with the medical examiner. The delay is not a sign that something went wrong — it reflects how much work goes into getting the answer right.