Toxins are substances created by plants and animals that are poisonous to humans. Toxins also include medications that are helpful in therapeutic doses but poisonous when used in an excess amount. Most toxins that cause problems in humans are released by microorganisms such as bacteria.
Reviewed By: David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.