Strychnine is a white alkaloid with a crystalline structure which is extracted from Nux Vomica and related plants. In small doses, strychnine has been used historically as a stimulant in both humans and animals; in larger doses, strychnine is fatal. It is also a common ingredient in pesticides, which is a concern for some people since strychnine may be ingested by unintended victims, such as neighborhood dogs.

Nux Vomica is a tree native to Southeast Asia. The seeds are the primary source of strychnine, although the tree's bark also contains small amounts of toxic alkaloids. Strychnine has been used historically for centuries. Nux Vomica is frequently prescribed in homeopathy, in the form of a highly diluted medicine which contains negligible amounts of strychnine. People have also used this compound as a stimulant; athletes, for example, took strychnine at the turn of the 20th century to improve their performance. Strychnine has been linked with several accidental deaths due to this practice; modern athletes generally do not use it as a performance aid because of the risks.

The fatal dosage of strychnine is not very large. When an animal ingests a fatal dose, the result is a rapid onset of spasms, muscle contractions, and lack of muscle control. One of the characteristic signs of strychnine poisoning is an arched back, and the instant appearance of rigor mortis after death. Most cases of death are caused by respiratory spasms which cut off the victim's air supply.

There is no antidote to strychnine poisoning, although several substances can be used to treat it. Some doctors may use activated charcoal to try and flush the toxin out of the patient, and historically tannin was used in an attempt to neutralize the strychnine so that the patient could express it safely. Modern treatment for strychnine poisoning also includes intravenous fluids and drugs to treat the painful muscle spasms associated with the condition.

Humans can ingest strychnine by breathing it, absorbing it through their skin, swallowing it, and through ingestion. If someone starts to display signs of strychnine poisoning, seek medical attention immediately. Rapid medical care is crucial to help a patient survive; the same goes for animals who ingest strychnine accidentally. People with household pets or a large concentration of neighborhood animals may want to to consider the use of traps for pests, rather than poisonous substances like strychnine, to avoid tragic accidents. In any case of poisoning, try to bring a sample of the poison with you so that medical personnel can test it.