For better or worse, these researchers changed science With the marvels of modern medicine, it’s easy to forget that much of it was once unknown. In fact, some of today’s top medical treatments (like spinal anesthesia) and bodily processes (like our metabolisms) only came to be understood through self-experimentation — that is, scientists who dared to “try it at home.” While we’re fortunate now to have highly regulated clinical trials, this wasn’t always the case. Sometimes bold, sometimes misguided, these seven scientists undertook experiments on themselves and contributed to the medical field as we know it today.

Santorio Santorio (1561–1636) Born in Venice in 1561, Santorio Santorio contributed a lot to his field while working as a private doctor to noblemen and later as the chair of theoretical medicine at the then-lauded University of Padua — including one of the first heart rate monitors. But his biggest claim to fame was his intense obsession with weighing himself. He invented an enormous chair he could sit on to monitor his weight. His endgame was to measure the weight of every meal he ate and see how much weight he lost as it digested. As strange as it sounds, he was meticulous, and his measurements were exact. He took detailed notes of how much he ate and how much weight he lost each day, eventually concluding that he lost half a pound each day between mealtime and toilet time. Unable to account for how his “output” was less than his intake, he initially chalked this up to “insensible perspiration,” meaning we breathe and sweat out some of what our body digests as invisible substances. That hypothesis was somewhat foggy at the time, but we now know he had early insight into the process of metabolism. Nearly every physician today can thank Santorio for laying the foundation for our understanding of this crucial bodily process.

John Hunter (1728–1793) Not all self-experiments go so well, though. In the 18th century, London’s population had grown massively. As sex work became more popularized and condoms weren’t yet in existence, sexually transmitted diseases (STDs) spread faster than people could learn about them. Few people knew how these viruses and bacteria worked beyond their transmission through sexual encounters. No science existed on how they developed or if one was related to another. John Hunter, the physician better known for helping invent a smallpox vaccine, believed the STD gonorrhea was just an early stage of syphilis. He theorized that if gonorrhea could be treated early, it would prevent its symptoms from escalating and becoming syphilis. Making this distinction would prove critical. While gonorrhea was treatable and not fatal, syphilis could have life-changing and even deadly ramifications. So, the passionate Hunter put fluids from one of his patients with gonorrhea into self-inflicted cuts on his penis so he could see how the disease ran its course. When Hunter started showing symptoms of both diseases, he thought he’d made a breakthrough. Turns out, he was very wrong. In reality, the patient he allegedly took the pus from had both STDs. Hunter gave himself a painful sexual disease and hindered STD research for nearly half a century unopposed. Worse yet, he had convinced many physicians to simply use mercury vapor and cut off infected sores, believing it would stop syphilis from developing. More than 50 years after his “discovery,” Hunter’s theory was finally disproved when the French physician Philippe Ricord, part of a growing number of researchers against Hunter’s theory (and his controversial method of introducing STDs to people who didn’t have them), rigorously tested samples from lesions on people with one or both diseases. Ricord ultimately found the two diseases to be separate. Research on these two STDs advanced exponentially from there.

Daniel Alcides Carrión (1857–1885) Some self-experimenters paid the ultimate price in pursuit of understanding human health and disease. And few fit this bill as well as Daniel Carrión. While studying at the Universidad Mayor de San Marcos in Lima, Peru, medical student Carrión heard about an outbreak of a mysterious fever in the city of La Oroya. Railroad workers there had developed severe anemia as part of a condition known as “Oroya fever.” Few understood how this condition was caused or transmitted. But Carrión had a theory: There might be a link between the acute symptoms of Oroya fever and the common chronic “verruga peruana,” or “Peruvian warts.” And he had an idea for testing this theory: injecting himself with infected wart tissue and see if he developed the fever. So that’s what he did. In August 1885, he took diseased tissue from a 14-year-old patient and had his colleagues inject it into both his arms. Just over a month later, Carrión developed severe symptoms, like fever, chills, and extreme fatigue. By the end of September 1885, he died from the fever. But his desire to learn about the disease and help those who contracted it led to extensive research over the following century, leading scientists to identify the bacteria responsible for the fever and learning to treat the condition. His successors named the condition Carrión’s disease to memorialize his contribution.

David Pritchard (1941–) If drinking gut bacteria wasn’t bad enough, David Pritchard, a professor of parasite immunology at the University of Nottingham in the United Kingdom, went even further to prove a point. Pritchard taped 50 parasitic hookworms to his arm and let them crawl through his skin to infect him. Chilling. But Pritchard had a specific goal in mind when he undertook this experiment in 2004. He believed that infecting yourself with Necator americanus hookworms could make your allergies better. How did he come up with such an outlandish notion? The young Pritchard traveled through Papua New Guinea during the 1980s and observed that locals who had this type of hookworm infection had far fewer allergy symptoms than their peers who didn’t have the infection. He continued to develop this theory over nearly two decades, until he decided it was time to test it — on himself. Pritchard’s experiment demonstrated that mild hookworm infections could reduce allergy symptoms by calming down the body’s immune response to allergens that would otherwise cause inflammation, like those resulting in conditions like asthma. Numerous studies testing Pritchard’s theory have since been conducted, and with mixed results. A 2017 study in Clinical and Translational Immunology found that hookworms secrete a protein called anti-inflammatory protein 2 (AIP-2), which can train your immune system to not inflame tissues when you inhale allergy or asthma triggers. This protein may be usable in future asthma treatments. But a 2010 study in Clinical & Experimental Allergy was less promising. It found no real impact from hookworms on asthma symptoms besides very minor improvements in breathing. At the moment, you can even get shot up with hookworms yourself — for the affordable price of $3,900. But if you’re at the point where you’re considering hookworms, we recommend following more proven allergy treatments, such as allergen immunotherapy or over-the-counter antihistamines.

August Bier (1861–1949) While some scientists change the course of medicine to prove a compelling hypothesis, others, like German surgeon August Bier, do so for the benefit of their patients. In 1898, one of Bier’s patients at the Royal Surgical Hospital of the University of Kiel in Germany refused to undergo surgery for an ankle infection, as he’d had some severe reactions to general anesthesia during past operations. So Bier suggested an alternative: cocaine injected directly into the spinal cord. And it worked. With cocaine in his spine, the patient stayed awake during the procedure without feeling a lick of pain. But a few days after, the patient had some terrible vomiting and pain. Determined to improve upon his finding, Bier took it upon himself to perfect his method by asking his assistant, August Hildebrandt, to inject a modified form of this cocaine solution into his spine. But Hildebrandt botched the injection by using the wrong needle size, causing cerebrospinal fluid and cocaine to pour out of the needle while still stuck in Bier’s spine. So Bier got the idea to try the injection on Hildebrandt instead. And it worked. For several hours, Hildebrandt felt absolutely nothing. Bier tested this in the most vulgar ways possible. He pulled Hildebrandt’s hair, burned his skin, and even squeezed his testicles. While both Bier and Hildebrandt’s efforts gave birth to spinal anesthesia injected directly into the spine (as it’s still used today), the men felt terrible for a week or so afterward. But while Bier stayed home and got better, Hildebrandt, as the assistant, had to cover for Bier at the hospital during his recovery. Hildebrandt never got over it (understandably so), and severed his professional ties with Bier.

Albert Hofmann (1906–2008) Even though lysergic acid diethylamide (better known as LSD) is often associated with hippies, LSD is becoming increasingly popular and more closely studied. People are taking microdoses of LSD because of its purported benefits: to be more productive, stop smoking, and even have otherworldly epiphanies about life. But LSD as we know it today likely wouldn’t exist without Albert Hofmann. And Hofmann, a Switzerland-born chemist who worked in the pharmaceutical industry, discovered it completely by accident. It all started one day in 1938, when Hofmann was humming away at work at Sandoz Laboratories in Basel, Switzerland. While synthesizing plant components for use in medications, he combined substances derived from lysergic acid with substances from the squill, a medicinal plant used for centuries by the Egyptians, Greeks, and many others. At first, he did nothing with the mixture. But five years later, on April 19, 1943, Hofmann was experimenting with it again and, thoughtlessly touching his face with his fingers, accidentally consumed some. Afterward, he reported feeling restless, dizzy, and slightly drunk. But when he closed his eyes and started seeing vivid images, pictures, and colors in his mind, he realized that this strange mixture he’d created at work had unbelievable potential. So the next day, he tried even more. And while he rode his bicycle home, he felt the effects all over again: the first true LSD trip. This day is now known as Bicycle Day (April 19, 1943) because of how significant LSD would later become: A whole generation of “flower children” took LSD to “expand their minds” less than two decades later and, more recently, to explore its medicinal uses.