An antidote is something that specifically stops the effects of a poison. Most poisons actually have no antidote. That does not mean that no antidote exists, but rather that we simply have not discovered one that works. Fortunately, many of the most serious poisons that people are most likely to come into contact with typically have an antidote available. Even in the cases of poisoning where no antidote can be used, there are sometimes treatments such as hydration and general medical care that may help a poisoned patient survive.
Poisons are toxins that can be naturally occurring; man-made; or animal based, such as viper or spider venom. One naturally occurring poison for which there is no antidote is ricin, a substance found in the beans that are used to make castor oil. Ingesting castor oil may be safe, but eating the castor beans that produce the oil can cause ricin poisoning. Ricin is most likely to cause death if inhaled or ingested. Supportive medical care can sometimes save a person exposed to ricin, but that is considered a treatment rather than an antidote.
Mercury is a heavy metal that can cause severe illness, damage and death. Poisoning from mercury can sometimes be treated with lots of fluids and having the patient ingest activated charcoal, but those are not antidotes; they may be helpful treatments, but often are not. The damage caused by the poisoning, which can sometimes include blindness or organ damage rather than death, is typically permanent.
Many different animals, amphibians and reptiles use poisons to protect themselves from predators or use venom to kill prey. These toxins are often highly poisonous and sometimes potentially fatal to humans as well. Rattlesnakes and black widow spiders are two examples of poisonous creatures for which antidotes, fortunately, exist since they are fairly common in many populated areas. The puffer fish and the blue-ringed octopus, however, are two examples of highly poisonous creatures in the wild for which there is no antidote.
It is believed that there less than 50 different types of antidotes available, which is a number far lower than the number of toxins to which a person might be exposed. These antidotes, however, often work against several different types of poisons, rather than just one. Antidotes are typically either natural substances or man-made drugs. In some cases, a drug that is used to treat common illnesses can be used in different amounts to counteract a poison. One example is insulin, which is a drug commonly used to treat diabetes but that can also be used as an antidote for certain types of drug overdoses.