Medicinal Poisons

The difference between a medicine and a poison should be as clear as day and night, but often what can cure can also kill, and notorious poisons such as arsenic and cyanide can also make useful drugs. The margin between an effective dose and toxic one is known as the therapeutic index, and it can sometimes be as narrow as a razor's edge.

Here are some examples of substances with the power to both harm and heal.

Arsenic

Arsenic is found in naturally occurring compounds, and one of history's best-known poisons. It is colorless, tasteless, and odorless; less than 1/10 of an ounce (2.8 grams) will cause acute poisoning. Arsenic wreaks havoc in the body by disrupting the electron transport chain and inhibiting the production of ATP – the molecule that all cells rely on for energy. A large dose of arsenic causes nausea, vomiting, diarrhea, hemorrhaging, and death. Smaller amounts, taken over a long period of time, result in weakness, confusion, and paralysis.

During the Italian Renaissance, members of the Borgia family used arsenic in wine to dispatch powerful rivals. Arsenic was also known as the poudre de succession (the powder of succession), since ambitious princes could eliminate younger rivals by feeding small amounts of arsenic to a wet nurse, and causing the poison to be secreted in breast milk. Arsenic poisoning is one of the most popular theories for Napoleon Bonaparte's death, because trace amounts of the poison was found in a sample of his hair. And many people are familiar with Arsenic and Old Lace, a story about a pair of homicidal maiden aunts. In more recent times, unintentional arsenic poisonings have occurred as a result of its use as a green pigment in paints, and as a result of ingesting wood ash from timber treated with chromated copper arsenate (CCA).

What most people don't realize is that arsenic has been used as a medicine for just as long as it's been used as a poison. In the fifth century BCE, Hippocrates used arsenic to treat ulcers. In 1786, arsenic became an ingredient in Fowler's solution, a tonic that, over the next 150 years, was prescribed for everything from asthma to cancer. In 1890, Sir William Osler prescribed arsenic trioxide as the best treatment for leukemia, and it's still used to treat acute forms of the disease today. In 1910, an arsenic compound became the first effective cure for syphilis, and arsenic derivatives are still used today to treat African sleeping sickness.

Cyanide

Thanks to countless mentions in movies and novels such as Agatha Christie's Sparkling Cyanide, cyanide is one of the most notorious poisons. Cyanide is part of a large group of compounds, and can occur in nature or be synthesized in the lab. Not all forms are poisonous.

Potassium cyanide, sodium cyanide, and hydrogen cyanide are all poisonous gases. Hydrogen cyanide was a major component of Zyklon B, the poison gas used by the Nazis to kill concentration camp prisoners (and is found in tobacco smoke!). Both the Soviet Union and the United States stockpiled cyanide as a chemical weapon during the 1950s and 1960s, but thankfully never deployed them as a weapon of war. In its solid form, cyanide salts can be used as a fast-acting suicide device. Spies have carried cyanide pills as a last resort in the event of capture; and perhaps it's a form of poetic justice that Hitler committed suicide using the same poison that claimed so many lives during the Holocaust.

Despite its well-deserved infamy, cyanide does have a few medical applications. The cyanide compound sodium nitroprusside can quickly lower a patient's blood pressure in an emergency, and is also used as a vasodilator in research.

Botulinum Toxin and Botox

Botulinum toxin is a neurotoxin that is the world's most poisonous naturally occurring substance, and a single gram of it is enough to kill 20 million people. The substance is produced by the bacteria Clostridium botulinum (the same bacteria that causes botulism), and in the last few years, there have been concerns that botulinum toxin may be used as a terrorist weapon. However, because it is made only in oxygen-deprived environments, it is difficult to produce.

Botox contains extremely dilute amounts of botulinum toxin, and has many medical applications. It is best known as a cosmetic treatment, where a single injection is used to relax muscles at a specific site to temporarily reduce the appearance of wrinkles. Botox injections can also treat migraines, crossed eyes, urinary incontinence resulting from spinal cord injuries, and spastic contractions caused by multiple sclerosis and cerebral palsy.

Botox is also useful in alleviating dystonia, a condition where misfiring of the brain causes abnormal and involuntarily muscle contractions. Scott Adams, the creator of the Dilbert comic strip, is one success story. For months, Adams suffered from spasmodic vocal dystonia, and until regular botox injections to the throat alleviated the condition, he could not speak at a normal volume. Concert pianist Leon Fleisher is another case. His performing career ended abruptly when dystonia struck, causing the fingers of his right hand to curl under involuntarily. Although botox is not a cure for the condition, after receiving bi-annual injections, Fleisher has the full use of his right hand, and he recently released his first two-handed recording in 40 years.

Chemotherapy

Chemotherapeutic agents are used to treat cancer, autoimmune diseases, and some chronic viral infections. Since cancer cells multiply much faster than normal cells, chemotherapy aims to kill cancer cells by preventing them from dividing or making new DNA. The downside is that healthy cells will be killed as well, and fast-dividing cells (including bone marrow, the lining of the digestive system, and the cells in the hair follicle) are hit the hardest. The side effects of chemotherapy include vomiting, diarrhea, fatigue, hair and weight loss, organ damage, and a suppressed immune system. And on top of all that, most chemotherapeutic drugs are also carcinogenic! However, chemotherapy is one of the best tools currently available in the fight against cancer.

Aconite

Aconite has been a well-known poison since ancient times, and is derived from plants in the Aconitum genus (common names include aconite, monkshood, or wolfsbane). Aconite can cause death by respiratory and heart failure. However, it can also relieve pain, inflammation, dilate blood vessels, and act as an anesthetic. It is often used in homeopathy and traditional Chinese herbal medicine.

Digotoxin and Digitalis

Digotoxin is extracted from plants of the digitalis genus, commonly called foxglove. But because just a nibble of the plant's leaves can be enough to cause death, they also have more sinister nicknames, including "Dead Man's Bells" and "Witches' Gloves." However, the same toxin that kills the heart can be turned into drugs (known as digitalis or digoxin) to treat heart conditions. Digotoxin is useful for treating atrial fibrillation, atrial flutter, and as a last resort medication for congestive heart failure.

Muscle Relaxants

Since the 1930s, muscle relaxants have been used during anesthesia, and to facilitate tracheal intubation. However, these drugs are often derived from dangerous substances. For example, the muscle relaxant curare is extracted from the Amazonian plants Strychnos toxifera and Chondrodendron tomentosum. Historically, the indigenous people of South America used extracts from these plants to make poison-tipped darts and arrows. Once hit, the poison paralyzes the prey, and quickly kills through asphyxiation.

Another frequently used muscle relaxant is Pancuronium bromide, a chemical compound sold under the brand name Pavulon. Pavulon is often used for muscle relaxation during general anesthesia. It was also used as a component in the chemical cocktail used for lethal injections of death row inmates, and as a murder weapon by serial killer Efren Saldivar, a respiratory therapist who was convicted of murdering several patients in California in the 1990s.

Coniine and Poison Hemlock

Hemlock (Conium maculatum) has been a known for thousands of years. In ancient Greece, hemlock was one means of doing away with those condemned to death, and the list of victims includes Socrates.

The most lethal compound found in hemlock is coniine, a neurotoxin that disrupts the central nervous system. However, hemlock also has sedative and anti-spasmodic properties, and Greek and Arab physicians used it to treat arthritis and other problems. But the difference between a therapeutic dose and a toxic dose is very small, and overdoses can cause paralysis, loss of speech, difficulty in breathing, and death.

Atropine

Atropine works by inhibiting the parasympathetic nervous system, and it is the active ingredient in deadly nightshade (Atropa belladonna) and other members of the plant family Solanaceae. During the sixteenth century, at considerable risk to their health, Italian women used extracts from these plants to dilate their pupils and give themselves a dreamy, wide-eyed appearance. Thus the plants were named belladonna, Italian for "beautiful lady." Historically, belladonna has also been used as an antidote to chloroform, opium, and the insecticide parathion. Atropine is an effective antidote for organophosphate and nerve gas poisoning, and is sometimes carried by soldiers in case of chemical weapons attacks. Injections of atropine are used to treat heart block, bradycardia (an extremely low heart rate) and cardiac arrest.

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If some of this information sounds alarming, remember that too much of just about anything can be dangerous! An overdose of vitamin D causes kidney damage, while too much vitamin A harms the liver, and even an excess amount of water or oxygen can harm the body!

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