Weird History

Major Medical Discoveries That Happened By Mistake

List Rules
Vote up the most surprising accidental medical discoveries.

Every year, millions of hours and billions of dollars are poured into medical innovation, with new methods of improving, sustaining, and extending human life discovered on a near daily basis - yet without some significant accidental medical discoveries thrown into the mix, many of us would not be here today.

Unintended scientific discoveries often prove more fascinating than those made on purpose. Perhaps it’s the lure of serendipity, or the enticing possibility of changing the world for the better through nothing more than sheer happenstance. Either way, people everywhere are grateful that some enterprising individuals were fortunate enough to stumble into important medical breakthroughs - and had awareness enough to understand the implications of their discoveries. 

  • The Coronary Angiogram Came About When A Catheter Slipped While A Cardiologist Was Treating A Patient
    Photo: Bleigass / Wikimedia Commons / CC BY-SA 3.0
    334 VOTES

    The Coronary Angiogram Came About When A Catheter Slipped While A Cardiologist Was Treating A Patient

    When F. Mason Sones Jr. accidentally invented the coronary angiogram (an X-ray to examine blood vessels), he didn’t just think he’d made a mistake - he thought he’d made a fatal error. At the time, the common belief was that contrast dye could be inserted into the larger vessels of the heart, like valves and chambers, but that putting it through the coronary arteries themselves would cause a lethal blockage.

    In 1958, Sones Jr. was overseeing the injection of dye into a patient’s aorta when the tube slipped into the right coronary artery, filling the vessel with contrast. Sones reportedly prepared for life-saving open-heart surgery, but the patient’s heartbeat - after a few ominous skips - kept chugging along. 

    Through further experimentation, scientists discovered that fears of blockages were overblown, and most patients could indeed manage a large amount of dye pushed through their arteries, leading directly to the invention of the coronary angiogram. 

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    581 VOTES

    Penicillin Was Discovered When A Scientist Decided Not To Throw Out A Moldy Petri Dish

    The discovery of penicillin has made an enormous impact on the world, and is perhaps the most famous tale of accidental medical innovation in history - even if the commonly told version of the tale is a touch apocryphal. Alexander Fleming did not, as is commonly reported, leave a sandwich or some other item sitting in his lab while on vacation, only to return and find it molded over with a life-saving substance, but the truth is not far off.

    Fleming did go on vacation in 1928, and he did leave some items out in the lab, but they were Petri dishes filled with colonies of Staphylococcus. When he returned, he started examining them, including one that had grown moldy in his absence - and that’s when he made the discovery of a lifetime. The area of the dish affected by the mold, which Fleming later identified as Penicillium notatum, was free of the Staphylococcus, as if something in the mold itself was inhibiting the growth and spread of the bacteria. Soon enough, Fleming proved that that was exactly what was happening, and as a result penicillin is now the most widely used antibiotic in the world. 

  • The Pap Smear As A Way To Test For Cancer Was Discovered During A Study Of Changes During The Course of Sexual Development
    Photo: Dr. Roshan Nasimudeen / Wikimedia Commons / CC BY-SA 3.0
    446 VOTES

    The Pap Smear As A Way To Test For Cancer Was Discovered During A Study Of Changes During The Course of Sexual Development

    The Pap smear is one of the simplest procedures in modern medicine, yet one of the most vital for maintaining female health. It all stems from one doctor, George Papanicolaou, and his desire to understand the menstrual cycle. 

    At first, Papanicolaou only intended to swab his test subjects’ vaginas to determine how their vaginal cells changed at different stages of sexual development. But when he noticed cancer cells in one such swab, the focus of his research shifted - and he soon discovered that this simple, inexpensive procedure provided the earliest possible indications of cervical cancer in patients. In doing so, Papanicolaou undoubtedly saved countless lives, and today the method still bears his mercifully shortened name. 

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    291 VOTES

    X-Rays Were Discovered During A Study Of Cathode Ray Tubes

    In 1895, Wilhelm Roentgen was performing a mundane experiment in Wurzburg, Bavaria - but the results he achieved were anything but. Roentgen was attempting to find out if cathode rays could pass through glass, so he covered a cathode tube with heavy black paper and waited to see what would happen.

    From within, an unnatural green light emerged through the paper and projected onto a nearby fluorescent screen, and that surprising result gave Roentgen an idea. He discovered that some of the rays he produced could pass through just about anything, but they also left shadows of solid objects on the screens they were projected onto. Because he didn’t know what these specific rays were, he labeled them “X-rays” - and the rest is history.