What I Do as a Medical, Forensic, Occupational, and Environmental Toxicology Expert Witness

Toxicology sits at the intersection of medicine, chemistry, public health, and law. When someone is injured, impaired, poisoned, or dies after an exposure to a drug, chemical, or environmental agent, the central legal question is almost always the same: What actually caused this, and how much did it matter?

That is where I come in.

As a board-certified Emergency Physician and consulting Toxicologist, I serve as an expert witness for both defense and plaintiff attorneys in cases involving drugs, poisons, and hazardous exposures. My role is to evaluate the medical and scientific evidence, determine what really happened biologically, and translate that into clear, defensible opinions that can withstand scrutiny in deposition and in court for plaintiff or defendant.

My practice spans four major domains of Toxicology:

Medical Toxicology — how drugs and poisons affect the human body
Forensic Toxicology — how substances are detected, measured, interpreted and misinterpreted in legal cases, and whether they caused or contributed to fatalities
Occupational Toxicology — workplace exposures and their acute and chronic health effects
Environmental Toxicology — toxic and biological substances in air, water, food

In real-world cases, these domains often overlap, and often involve Public Health, a discipline where I’ve gained additional certification (MPH, Masters of Public Health).

Drug and Alcohol–Related Cases

A large portion of my work involves alleged impairment, overdose, or death related to pharmaceuticals, alcohol, and drugs of abuse. These cases require far more than simply reading a lab report.

I evaluate:

• Blood, urine, and tissue drug concentrations
• Timing of exposure and sampling
• Metabolism and elimination, and do complex calculations
• Tolerance, chronic use, and withdrawal
• Drug-drug interactions
• Clinical signs and symptoms
• EMS, hospital, and autopsy records, and matter related to EMTALA

This includes cases involving alcohol, cocaine, methamphetamine, MDMA, opiates and fentanyl, prescription sedatives and stimulants, designer drugs, and cannabis. Whether the issue is DUI, an in-custody death, a workplace incident, or a medical malpractice claim, the core question is not “Was a drug present?” but “Was the drug actually causing impairment, injury, or death at that moment?”

That distinction is frequently misunderstood by courts, police, prosecutors, and even laboratory toxicologists. My job is to correct that.

In-Custody Deaths and Police-Related Cases

Deaths in custody — in jails, holding cells, emergency departments, or during police encounters — often involve complex toxicology. Individuals may have intoxicants on board, be in withdrawal, be hyperthermic, agitated, psychotic, or suffering from excited delirium, overdose, or metabolic collapse. They may have co-existing medical problems or suffer from polypharmacy.

I analyze how substances such as stimulants, opioids, sedatives, and alcohol interact with stress, restraint, dehydration, hyperthermia, and underlying disease. These cases demand a physician who understands both the pharmacology and the physiology of dying patients — not just a laboratory number.

Poisoning, Contamination, and Public Health Events

Not all toxicology is about drugs of abuse. I also evaluate cases involving:

• Accidental and intentional poisonings
• Food and water contamination
• Viral, bacterial, and parasitic outbreaks
• Heavy metals (lead, mercury, arsenic, etc.)
• Chemical exposures in homes, schools, and workplaces

These cases often involve allegations of negligence, product defects, unsafe facilities, or regulatory failure. I assess exposure pathways, dose, duration, biologic plausibility, and the medical timeline to determine whether a claimed injury is scientifically consistent with the alleged exposure.

Occupational and Environmental Toxicology

I regularly review cases involving:

• Industrial chemicals and solvents
• Pesticides and herbicides
• Fire smoke, soot, and combustion by-products
• Chronic mold exposure
• Post-fire building contamination
• Indoor air quality
• Workplace toxins

These claims often hinge on whether an exposure was sufficient in dose, duration, and route to actually cause the reported symptoms or long-term illness. I bring both toxicologic modeling and real-world clinical medicine to those determinations.

Why Being an Emergency Physician Matters

What distinguishes my work is that I do not look at toxicology in isolation.

After decades of Emergency Medicine practice in Level I and II Trauma Centers, I understand how poisoned and intoxicated patients actually present, how they deteriorate, and how they recover — or don’t. I can correlate drug levels, exposure history, and environmental measurements with vital signs, lab values, neurologic and other physical findings, and autopsy results.

That allows me to answer the questions courts care about:

• Did this substance meaningfully contribute to what happened?
• Was it the primary cause, a contributing factor, or incidental?
• Could the outcome have occurred without it?
• Was the medical response appropriate?
• Does the timeline make physiologic sense?

This is how causation is established — or disproven.

From Case Review to Courtroom

My work includes comprehensive case review, written expert reports, deposition testimony, and trial testimony. I routinely identify flawed assumptions, misapplied toxicology, and overstated conclusions in police reports, laboratory interpretations, and opposing expert opinions.

My goal is simple: to bring rigorous, clinically grounded toxicology into the legal process, so that verdicts and settlements are based on what actually happened in the human body — not on speculation or misinterpreted lab results.

For additional information about Toxicology or to retain me as an Expert Witness please contact me.

Professional portrait of Dr. Barry E. Gustin, toxicology expert witness, wearing a suit with arms crossed, conveying confidence and expertise in medical and forensic toxicology.

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