Requesting examples from medicine of serendipitous, initially puzzling, discoveries

[profjmb]

I am an academic psychologist, and I have discovered a highly reliable difference between persons without and without paraphilias. (My query does not require understanding what paraphilias are.) This discovery was serendipitous, not hypothesis driven. (In case you're worried, I have followed it up carefully, with preregistered studies, and it holds.) My impression is that many useful medical findings were serendipitous and atheoretical. But I'm not a physician or medical historian, and can't come up with any I'm confident about. (Perhaps plaques in Alzheimer's, although I'm not sure how useful those have ultimately been, or how specific they are.)

Anticipating writing up the study, I'd like an example or three of situations in which a discovery was made this way–ideally the discovery would be some kind of indicator that differed between persons with and without a particular diagnosis–was not understood immediately, but ultimately proved useful.

I'm starting with "Microbiology and Immunology," because it seemed the most likely place where examples might be found.

Thanks in advance.

[CharonY]

I think it depends quite a bit on far one might want to stretch the terms. Drug discovery tends a bit on that side as often the discovery pipeline is often not quite as targeted as one might think. One might look for a compound that binds to a certain target but then the a use for it only emerges by some screening experiments with often unpredicted results. 

There are cases where these discoveries were hypothesis-driven. But the hypothesis was wrong. A historic example is potassium bromide. In the 19th century it was believed that masturbation might cause epilepsy and bromides were known to reduce the sex drive. So Charles Lockock speculated that using potassium bromide could curb the sex-drive, reduce masturbation and therefore reduce epipleptic convulsions. As it turned out, potassium bromide does indeed reduce convulsions, but obviously not by inhibiting masturbation. Potassium bromide had been in use as sedative and anticonvulsant into the 20th century until better drugs came along.

Another perhaps more prominent example is sildenafil (viagra) which originally was a candidate to dilate blood vessels in the heart and alleviating chest pain by blocking the phosphodiesterase type 5. But as we now know it actually dilated vesels elsewhere more effectively...

In the microbiological field there are certainly discoveries which came from observations and might as such be considered not based on a specific theory, but I am not sure whether that fits the bill quite as well, as in biology hypotheses where where often built after making empirical observations. A lot are thrown out and the few survivors might appear to be a chance finding, while in truth it is simply based on the scientific process.

[StringJunky]

 Would Alexender Fleming's accidental discovery of the antibiotic action of Penicillium notatum qualify?

[CharonY]

4 minutes ago, StringJunky said:

 Would Alexender Fleming's accidental discovery of the antibiotic action of Penicillium notatum qualify?

That is also a classic example, but in some ways it was also a very classic approach. Fleming sorted through petri-dishes and found that plates with mould there were clear zones. From there he formed the hypothesis that something was there inhibiting bacterial growth. On the one hand the plates probably not prepared with the express intention to identify inhibiting compounds, yet the first observation led more or less straight to the correct hypothesis. It goes to what I was thinking earlier, whether discoveries are truly serendipitous or whether it is more or less just the way it works.

[TheVat]

John Fewster, a country doctor, noticed farmers who had had cowpox seemed immune to smallpox.  Though his accounts were largely ignored, Edward Jenner heard them from the physician brothers to whom he was apprenticed (and who had met with Fewster) and years later developed a vaccine with Fewster's observations in mind.  Jenner then was credited with the now debunked lovely milkmaid story by a biographer eager to glorify Jenner as a singular genius struck by an epiphany.    

And there was Albert Hoffman, the chemist working on ergot derivatives and their efficacy for inducing uterine contraction, who found himself tripping one afternoon in his laboratory at Sandoz.  The derivative in question was the 25th he had synthesized, hence called LSD-25.

[Genady]

The discovery of the microbiology itself, by Leeuwenhoek was serendipitous and puzzling.

[profjmb]

Thanks to everyone who has responded so far! These are excellent fodder.