Toxicology of Abused Substances

The field of forensic toxicology familiar to most people is drug testing for athletes or job applicants, or alcohol testing for drivers suspected of driving under the influence. These tests are straightforward, designed to determine whether a person's system contains a certain substance, and how much. They are based on known relationships between the result of the test and the amount of the substance used. For instance, breathalyzer tests are based on the idea that a certain amount of alcohol in a person's breath coincides with a known amount of alcohol in their blood, which is the amount affecting their ability to drive.

A related field is that of postmortem toxicology, where samples taken from the deceased are tested. While a Medical Examiner performing an autopsy has access to more samples-for instance, blood and liver samples may be taken from the body of someone killed in a car accident and tested for alcohol-the interpretation of the results from these samples may be more difficult.

A breathalyzer test needs only to show the level of intoxication at the time the test is taken. A urine test for illegal drugs generally needs only show whether or not drugs were used, not how much. At autopsy, however, the critical information may be the blood alcohol content (BAC) at the time of death, or the amount of a particular substance used, to determine whether the substance contributed to the death. This is made difficult by many of the processes that occur after death. For example, bacteria that multiply in a body after death may produce alcohol, skewing the results by increasing the apparent blood alcohol content.

An experienced toxicologist, however, understands these complications and can perform multiple tests to verify his or her results. Vitreous humor, for instance, may be a more reliable indicator than blood of anti-mortem (before death) BAC because its alcohol content doesn't change after death.

Postmortem toxicology is frequently important in evaluating the cause of death, even if there isn't enough of a drug in the decedent's system to cause an overdose, because impairment due to drug or alcohol use can frequently contribute to the cause of death. The most obvious example of this is drunk driving, where intoxication may lead to a deadly collision, but other drugs may increase the danger of a situation as well.

Alcohol is the most thoroughly studied drug when it comes to impairment. Toxicologists can tell when a person was impaired by alcohol before death more easily than they can judge impairment by other substances-the presence of marijuana in urine, for example, indicates it was used in the past, but shows neither when it was used nor how it affected the user.

Since many kinds of substance abuse may lead to potentially dangerous impairment, and the effects on a user may be complicated if multiple interacting drugs were used, and since different users may be affected in different ways, more information is frequently needed than a simple quantity of a given drug found in the system. Witnesses may be needed to judge the behavior and apparent impairment of the user before death.

Purchase Museum Tickets
Family Page
Make a Difference
Become an Investigator
Visit our Crime Library
Join our Blog