poison

Introduction
Nature of a toxic substance
- Definition of a poison
- Classification of a poison
  - Classification based on origin
  - Classification based on physical form
  - Classification based on chemical nature
  - Classification based on chemical activity
  - Other classifications
- Transport of chemicals through a cell membrane
- Conditions of exposure
  - Routes of exposure and absorption of chemicals
    - Injection
    - Ingestion
    - Topical (skin)
    - Inhalation
  - Frequency of exposure
  - Dose of exposure
- Distribution of toxicants in the body
  - Role of the lymphatics
  - Role of the blood
  - Role of tissue blood flow
  - Role of protein binding
  - Role of distribution barriers
- Elimination of toxicants
  - Excretion
  - Biotransformation
- Therapeutic, toxic, and lethal responses
  - Morphological versus functional toxic responses
  - Local versus systemic toxic responses
  - Immediate versus delayed toxic responses
  - Reversible versus irreversible toxic responses
  - Chemically induced immune responses
    - Cellular and humoral immunities
    - Allergies
- Teratogenesis
- Carcinogenesis
- Mutagenesis
Types of poison
- Agricultural and industrial chemicals
  - Agricultural chemicals
    - Insecticides
    - Herbicides
    - Rodenticides
    - Plant growth regulator
  - Industrial chemicals
    - Organic compounds
    - Inorganic compounds
  - General air pollutants
- Drugs and health care products
  - Painkillers
  - Tranquilizers and sleeping pills
  - Antipsychotic drugs
  - Cold medications
  - Antiseptics
  - Vitamins and iron pills
  - Antidepressants
  - Drugs of abuse
  - Cardiovascular drugs
  - Antiasthmatics
- Poisons of biological origin
  - Importance to humans
  - Microbial toxins
    - Moneran toxins
    - Mycotoxins
    - Protistan poisons
  - Plant poisons (phytotoxins)
  - Animal poisons (zootoxins)
- Radiation
  - Radiation, radioactivity, and radioisotopes
  - Ionizing radiation
    - Radiation sources
    - Adverse effects of ionizing radiation
    - Toxicities of whole-body ionizing radiation
    - Local toxicities of common beta-particle emitters
    - Local toxicities of common alpha-particle emitters
  - Nonionizing radiation
    - Ultraviolet radiation
    - Infrared radiation and microwaves
    - Lasers

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At a Glance

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Related Questions

poison

biochemistry

Also known as: toxic chemical

Written by

Curtis D. KlaassenAll

Fact-checked by

Britannica Editors

Last updated

Oct. 26, 2026 •History

poison, in biochemistry, a substance, natural or synthetic, that causes damage to living tissues and has an injurious or fatal effect on the body, whether it is ingested, inhaled, or absorbed or injected through the skin. Although poisons have been the subject of practical lore since ancient times, their systematic study is often considered to have begun during the 16th century, when German-Swiss physician and alchemist Paracelsus first stressed the chemical nature of poisons. It...

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