What Is the Most Poisonous Chemical Compound?

Worst Poison in the World

Danger Hazardous Chemicals Sign on a Barrel
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When you get right down to it, everything is poisonous. Water will kill you if you drink too much of it. Oxygen is a deadly poison, yet we need it to live. However, there are some chemicals that we are better off not encountering. Here's a list of the most poisonous chemicals known. Keep in mind, toxicity varies from one species to another (i.e., what may be poisonous for a mouse may be more/less poisonous to a human) and within a species (i.e., age, sex, genetics all affect susceptibility to a toxin).

I've listed the name of the toxin, its source, approximate average lethal dose per kilogram of body weight (LD50), and the species.

  1. Tetanus: 1 nanogram/kg mouse, human
  2. Botulinal neurotoxin (bacteria): 1 nanogram/kg mouse, human
  3. Shigella (bacteria): 1 nanogram/kg monkey, human
  4. Palytoxin (coral): 60 nanogram/kg dog (iv)
  5. Diphtheria (bacteria): 100 nanogram/kg human
  6. Ricin (from castor beans): 1 microgram/kg human
  7. Aflatoxins (mold which grows on nuts, legumes, seeds): 1-784 micrograms, depending on type of aflatoxin duckling (oral)
  8. Shigella (bacteria) 1 microgram/kg mouse
  9. Saxitoxin (shellfish) 3-5 micrograms mouse (iv), about 50x higher dose orally
  10. Tetrodotoxin (fugu pufferfish) 10 micrograms mouse (ip)
  11. Diphtheria (bacteria) 1.6 milligram/kg mouse


  • Merck Index, 11th Ed., S. Budavari et al. (editors), Merck (1989) ISBN 911910-28-X
  • McGraw-Hill Concise Encyclopedia of Science and Technology, 2nd Ed., McGraw Hill (1989) ISBN 0-07-045512-0, CD-ROM