The Oxford English Dictionary defines Toxicology as "The science of poisons; that department of pathology or medicine which deals with the nature and effects of poisons". However, in practice, the term "poisons" includes drugs (prescription or non-prescription), alcohol and related substances.

Clinical Toxicology is the application of toxicology to the clinical management of patients. There are two primary areas: Emergency Toxicology and Therapeutic Drug Monitoring.

  • Emergency Toxicology involves the identification of poisons attending a medical treatment centre with suspected accidental or suicidal poisoning (by drugs or other toxins). The purpose is to rapidly identify poisons which can be actively treated.

  • Therapeutic Drug Monitoring involves measuring the serum or blood concentration of a drug which is being administered therapeutically. The purpose is to guide the physician is adjusting dosage so that the drug concentration is within the effective range.

Forensic Toxicology is application of toxicology for legal purposes. The primary areas are general Forensic Toxicology, Postmortem Toxicology, "Criminal" Toxicology, Workplace Drug Testing and Sports Drug Testing.

  • General Forensic Toxicology involves the detection and quantification of alcohol, drugs and other poisons in blood or other specimens for legal purposes. It may involve the dead (see below) or the living. For the living, where a crime is potentially involved, it may involve testing impaired drivers for the presence or alcohol or drugs. Or, it may for example, involve testing victims of sexual assault for sedative drugs to determine if the victim was "drugged" by the attacker.

  • Postmortem Toxicology involves the detection and quantification of alcohol, drugs and other poisons in blood, tissues and other specimens from those who died suddenly or unexpectedly (so-called coroner or medical examiner toxicology). The purpose is to determine whether drugs or poisons, if present, caused or contributed to the death.

  • Workplace Drug Testing involves the detection and quantification of specific classes drugs in urine from employees or applicants (usually amphetamines, cannabis, cocaine, opiates and phencyclidine). The purpose is to determine whether those persons have used any of the target drugs recently, and whether they may have a substance abuse problem.

  • Sports Drug Testing involves the detection and identification of specific classes of performance enhancing drugs in the urine of athletes (amateur or professional). While sports drug testing usually refers to the testing of human athletes, it also applies to the equally specialized areas of horse (equine) and greyhound racing.