A forensic toxicologist evaluates chemical levels in the body to help determine facts about poisoning, drug use and cause of death. They identify foreign, toxic or otherwise hazardous chemicals that negatively effect the body. Some of the substances that can be identified during an evaluation include alcohol, illegal narcotics, prescription pills, poisons, metals, gases and other measurable chemicals.

Investigations include the examination of tissue samples and bodily fluids. This requires attention to detail and a natural understanding of bodily functions, as chemicals rarely remain intact once the body ingests and metabolizes them. Forensic toxicologists commonly work with urine, blood, hair and oral samples. However, when bodies are compromised, such as with decomposition, forensic toxicologists may sample the vitreous humor to detect chemicals. In more extreme cases, bacteria or maggots taken from the body can be studied, since these organisms are likely to have ingested the chemicals.

Work is generally performed in a lab using state-of-the-art tools, chemical reagents and strict methodologies. The findings can shed light on a person's physical state at the time of a crime or even the cause of his death. When a crime has taken place, forensic toxicologists use medical technology and tools to help tie together physical symptoms with crime scene evidence. Relevant crime scene evidence may include pill bottles, trace residue, powders and the presence of pre-identified chemicals. Samples gathered at a crime scene usually serve as a jumping-off point for a forensic toxicologist.

Forensic toxicologists' work is usually part of a group effort. As law enforcement officers, forensic pathologists and other crime scene investigators work to piece together a scene, a forensic toxicologist offers his findings as part of the puzzle. Likewise, while a forensic toxicologist is usually perceived as someone who determines what is present in the body, his job also involves determining what is not present in the body. An absence of chemicals can be just as significant, though typically, forensic toxicologists choose tests to perform based on what chemicals are suspected to be found.

Forensic toxicologists can be licensed by the American Board of Toxicology, the American Board of Clinical Chemistry and the American Board of Forensic Toxicology. They may work in law enforcement, but they may also be hired to do work for employers and those involved with animals and sports. Regardless of who hires the forensic toxicologist, their goal remains the same: to identify the absence or presence of chemicals in bodies.