5 Deadly Poisons That Are Also Medicine, From Cancer Therapy to Heart Disease Drugs

Doctors throughout history have used some pretty funky substances for medicinal purposes, like the ancient Egyptians who mixed crocodile poop with honey and inserted the concoction into vaginas as a weird form of birth control. But excrement is just the tip of the iceberg — modern medical professionals use known poisons to treat their patients’ maladies even today.

Arsenic

This element itself can cause cancer, as well as other health problems, but that doesn’t mean it can’t also cure cancer. Arsenic, which can be found in nature as well as in pesticides, building products and some industrial processes, has been used for medical treatment in previous eras, like to treat syphilis in Victorian times, according to the American Cancer Society. It is poisonous in high doses, the society notes, but it is still used now to treat a rare blood cancer called acute promyelocytic leukemia. That cancer is associated with serious bleeding and clotting problems, and arsenic may be used in patients whose bodies for whatever reason cannot tolerate the more usual route, a class of chemotherapy drugs called anthracyclines.

Read: The History of Poop's Use In Medicine

Foxglove

For people with heart failure, digoxin can be a lifesaving drug that strengthens the heart, controls its rhythm and improves circulation, according to the Mayo Clinic. It is also derived from a potentially lethal plant called foxglove. The National Gardening Association describes the biennial plant as having “tall, dramatic spikes of tubular flowers with speckled throats” that could be pink, red, purple, white or yellow. It is considered poisonous because its leaves when consumed can cause low blood pressure and an irregular heartbeat, as well as confusion, depression or lethargy, hallucinations, headaches, vision problems, vomiting, diarrhea or a rash. The U.S. National Library of Medicine notes those symptoms vary depending on the period of time over which a person was poisoned.

Radiation

This popular form of treatment essentially works by murdering cancer cells. The National Cancer Institute explains doses of high-energy radiation, which can be x-rays, gamma rays, or radioactive substances, are used to shrink tumors in roughly half of all patients. They are effective because they damage the DNA of the cancer cells, killing them or making them inactive. But radiation is also dangerous for healthy cells, which is why there are so many side effects to this cancer treatment, like skin problems and fatigue.

High doses of radiation are lethal. Radiation sickness of a low magnitude can cause vomiting and peeling skin, while extreme exposure causes extreme swelling and blackens and blisters skin before it sloughs off completely.

Read: Radiation Killed The Nazis In Indiana Jones

Yew plant

Another potentially toxic cancer treatment is the yew tree. The American Museum of Natural History in New York notes that while the “seeds, leaves, and bark are highly poisonous to humans,” the Pacific yew tree’s bark contains a harmful ingredient that on a cellular level can be used to stop certain cancers from progressing, like breast and lung. For people with a stent in their coronary arteries — a supportive tube in the vessel that reopens blood flow — the derived medicine can also prevent those arteries from re-narrowing. “The drug is a prime example of the use of poisons in the service of medicine, a challenge to the modern view of poison as an instrument of death, whether by accident, suicide, or murder most foul.”

Snake venom

Thousands of animals on Earth produce venom, but they are not all bad. According to the AMNH, the African saw-scaled viper’s venom was used to create the blood thinner tirofabin. It’s not alone: Discover magazine says there are several “venom-derived pharmaceuticals on the internation market.” Captopril, which is used to treat high blood pressure, heart failure and diabetes-caused kidney problems, can be traced back to venom from the Brazilian viper. The diabetes drug exenatide helps the body produce insulin and comes from the venomous saliva of a lizard, the Gila monster that is indigenous to the southwestern United States and northwestern Mexico.