Mercury: The “Cure” That Killed

For at least two years before his death, Keats was taking mercury as a treatment for his illness. During the 19^th century, this heavy metal was a common ingredient in remedies for ailments like tuberculosis and syphilis, as well as dysentery, rheumatism, and others. Although it is clear that the poet died from his disease, historians and biographers have suspected mercury poisoning impacted his final years, especially as it can lead to hair loss, gastrointestinal distress, and mood swings, all of which he appears to have experienced.

There are few substances in the history of medicine with a more fascinating and deadly story than mercury, as Keats’ sad tale illustrates. In fact, Keats was not the only 19^th century luminary to be potentially poisoned by his treatments. Edgar Allan Poe, the American poet, may have also suffered from mercury poisoning after seeking treatment when exposed to cholera in July 1849. Poe was prescribed calomel (mercury chloride), which may have caused him issues before his death. However, it is not possible to say it killed him, as the mercury levels were too low, even at their highest concentrations.  

For centuries and across cultures, the silvery metal has been regarded as having almost preternatural qualities, which has regrettably meant that many people have consumed it in some way, often to their detriment. But how did something we know to be so toxic today become such a common feature of medicine?

Mercury in ancient civilizations

I’m not going to lie, the early history of mercury and medicine is tricky to pin down despite its significance and wider use among different cultures. For instance, we know that cinnabar – naturally occurring mercury sulfide ore, the source for the liquid metal mercury (sometimes referred to as quicksilver or liquid silver) – was used for supposed spiritual and ritual purposes by multiple ancient peoples. Cinnabar (HgS) was highly valued by the ancient Greeks, Romans, Chinese, Persians, and Hindus, and the cultures in pre-Columbian America.

The mineral, also known as “vermilion”, appears in a rich red color (think of the rich red on the walls of buildings in Pompeii), and so served as a pigment for decorations, luxury items, and funerary goods. However, it was also an ingredient for certain medicines in ancient Tunisia, India, Oman, Japan, and China. Within these contexts, it was used in treatments for various problems, including fevers, insomnia, lice, stroke, trauma, and mouth ulcers.

Among the Taoist alchemists of ancient China, cinnabar, separated mercury, as well as lead, sulfur, and arsenic were used in so-called elixirs of life – remedies designed to prolong life or even produce immortality. For instance, Qin Shi Huang, the First Emperor of China, was so worried about death that he frantically desired a route to immortality and consulted every physician, magician, and sage who may have been able to help him. Unfortunately for the emperor, one of the elixirs he turned to allegedly contained mercury. It is thought to have eventually killed him (I’m sure the irony is not lost on anyone).

Within Western cultures, the relationship between mercury and medicine is a little less clear. The oldest evidence of mercury poisoning – which presents with tremors, mood changes, hearing and vision loss, insomnia, headaches, and cognitive issues, among other symptoms – has been dated to around 5,000 years ago, during the Copper Age in Iberia. Here, cinnabar was mined as a pigment for paint and may have been used in medicine and drugs as well, though this is far from certain.

It is known that the ancient Greeks and Romans used mercury in their cosmetic products, though it is unclear to what extent they included it in their medical treatments. We do know that the more learned medical thinkers were aware of its toxicity. For instance, the medical works of Galen, the famous Roman and Greek physician, do not include anything on mercury because of its dangers. However, by the seventh century CE, Paul of Aegina, a Byzantine physician, discouraged the use of mercury substances in medicine as they were lethal, but he did acknowledge that some people consumed it by mixing its ash with other substances to treat colic.

Following the collapse of the Roman Empire, the body of Greek and Roman medical works were lost to Europeans until they were translated and developed by Arabic scholars during the “Islamic Golden Age” (between the 10^th and 12^th centuries CE). Within the works of individuals like al-Rhazes, Ibn al-Jazzār, Avicenna, Abū l-ʿAlāʾ Zuhr, and Muḥammad al-Idrīsī, mercury was included as a topical treatment for skin conditions. It is possible that the substance was incorporated into their medical recipes due to influences from Indian Ayurvedic traditions.

The alchemist with a big idea and a bigger name

The story of mercury’s relationship with learned medicine became more obvious in the 16^th century due to the influence of a man with an incredible name. According to the work of the Swiss physician, alchemist, and philosopher, Paracelsus (born Philippus Aureolus Theophrastus Bombastus von Hohenheim), Hippocratic/Galenic medicine was too heathen to be accepted. So, in true Reformation spirit, he set out to create a Christian medical tradition that ended up emphasizing the use of chemicals and minerals in the treatment of disease.

Whereas the Greek medical tradition conceived of the human body as being made up of four elements (earth, air, fire, and water), Paracelsus saw it as consisting of three primary substances: salt, sulfur, and – you guessed it – mercury.

Although this new way of thinking was heavily informed by spiritual principles (salt represented solidity and the body, sulfur was metallicity and the soul, and mercury was liquidity and the spirit), it was also very practical. Rather than believing that disease was the result of an internal issue – the body’s humors being out of balance – Paracelsus thought illness came from external forces that assailed the body. These forces came from various places, including poison emanations in the air, from the Earth, or even the stars.

This meant each illness was believed to have a distinct and discrete cause, which, as he understood it, could be treated by chemical preparations.

One significant illness that received a targeted treatment was syphilis. Although its origins are still unknown, today we understand syphilis to be a sexually transmitted bacterial infection that can be treated with antibiotics. However, in the 16^th century, it was a terrifying and mysterious disease that seemed to come from nowhere.

The disease has four stages of progression, three of which present with painless ulcers or chancres. In the first stage, these marks appear on or around the genitals. In the second phase, blotchy red rashes appear, often around the hands and soles of the feet. These symptoms can be accompanied by hair loss. After this, patients can experience a latent stage where they present with no symptoms, a stage that can last for several years. If left to progress to the third stage, patients will experience overall physical deterioration, where their bones, skin, organs, nervous system, and cardiovascular system will experience extreme damage. In the past, people who reached this point were often shunned from society due to their disfigurement.

Because three of these stages presented on the skin, mercury became an obvious go-to treatment. Since the introduction of Arabic medical sources into Europe during the medieval period, mercury was used to treat skin conditions (including Leprosy). This, combined with Paracelsus’s influence, established mercury as the preferred treatment for syphilis. In fact, mercury remained the treatment option for syphilis for centuries.

But mercury is toxic, right, so how did they make medicine out of this substance? Well, the size of the dose, in this context, was the danger; substances like mercury, so Paracelsus believed, could be used in small, carefully calibrated amounts even though they were toxic in larger doses. So, mercury became a staple ingredient in ointments used to treat syphilis.

“One night with Venus, a lifetime with Mercury”

Over the years, mercury preparations began to expand in their forms as did the ailments they could supposedly treat (including melancholy, constipation, influenza, parasites, and even tuberculosis). It went from being in ointments for the skin to appearing in pills to be swallowed, elixirs to be drank, vapors to be inhaled, or solutions to be injected (namely mercury oxycyanide in the 19^th century).

Many mercury-based medicines were derived from calomel (mercury chloride), a seemingly innocuous, odorless white powder. If taken orally, calomel was particularly effective as a “cathartic”, which basically meant you “purged” your bowels into a toilet. This appealed to Hippocratic and Galenic medical ideas that were still current in society – namely that health could be restored by balancing the body’s humors through bleeding, emetics (vomiting), or a purgative (forcing you to have a bowel movement) like this. So, a (un)healthy dose of calomel made sense.

As mercury toxicity increases, people would also start to drool uncontrollably. You might think this was a negative for people taking the drug, but the opposite is true. As Lydia Kang and Nate Pedersen noted in their book Quackery: A Brief History of the Worst Ways to Cure Everything, Paracelsus himself believed the optimal effective dose for mercury was one that produced at least three pints of saliva – so to him, a little drooling was not something to spit at.

Mercury continued to be used for various illnesses throughout the 19^th century and well into the 20^th, especially for syphilis. As the medical community learned more about the causative agents behind disease, as well as the mounting evidence that the effects of heavy metal toxicity really did outweigh any benefits to the substance, mercury’s use fell out of favor.

It might be tempting to interpret this as an example of scientific knowledge winning the day, but remember this substance was championed for centuries, even though its negative effects were well known – even in the 1940s, calomel was still being given to children to ease teething pain.  

Historians of medicine have long debated the extent to which mercury really did help relieve patients’ symptoms or whether it just exacerbated the situation, deteriorating health and ultimately killing them earlier than syphilis would have if left “untreated”.