When scientists in New Zealand discovered that a meningitis vaccine fortuitously protects against gonorrhoea, they were benefiting from an unpredictable force responsible for some of history’s most striking medical breakthroughs: serendipity.

So many things have been discovered by chance. The German writer, scientist and all-round polymath Johann Wolfgang Goethe, a discoverer himself, wrote: “Discovery needs luck, invention, intellect – none can do without the other.”

Viagra

In pharmaceutical giant Pfizer’s laboratories in Kent, a failed treatment for angina accidentally became a billion-dollar erectile dysfunction blockbuster, and the world’s most famous blue pill.



During early clinical trials of sildenafil, now better known by its trade name Viagra, male volunteers taking the pills consistently reported unprovoked, long-lasting erections. After further investigation, it turned out that Viagra, designed to relax blood vessels around the heart to improve blood flow, was having the same effect on arteries within the penis. Since its commercial release in 1998, it has been used to improve the sex lives of millions of men worldwide.



Incidentally, the 2007 ‘Ig’ Nobel Prize, awarded annually for that year’s most useless research, was awarded to three Argentinian scientists who discovered that Viagra helped hamsters recover faster from jet-lag.



Penicillin

Returning to work after a month-long Scottish vacation in 1928, pathologist Alexander Fleming made a discovery in a discarded culture dish, which he had unintentionally left open to the elements on a window sill in his laboratory at St Mary’s Hospital in London.



In Fleming’s absence, the dish, growing the dangerous bacteria Staphylococcus aureus, had become contaminated with an air-borne mould – a type of fungus. Fleming noticed that, near the blue-green strands of fungus, growth of the bacteria had been stopped in its tracks.



Fleming had inadvertently stumbled across the first antibiotic, which he called penicillin.



For his accidental discovery, he shared the Nobel prize for medicine in 1945 with Florey and Chain, Oxford chemists who perfected the process of penicillin mass production in time to treat infected battlefield injuries sustained in the second world war.



“When I woke up just after dawn on 28 September, 1928, I certainly didn’t plan to revolutionise all medicine by discovering the world’s first antibiotic, or bacteria killer,” Fleming later recalled. “But I suppose that was exactly what I did.”

Heart pacemaker

New York engineer Wilson Greatbatch invented the world’s first implantable heart pacemaker – but he didn’t mean to.

While trying to build a device to record heartbeats in 1956, he accidentally installed the wrong type of resistor into his prototype – which promptly began to emit regular electrical pulses.

Realising these pulses were recapitulating the electrical activity of a normal heartbeat, Greatbatch immediately saw the potential of his device. After two years of refinements, his design for a pacemaker that could be implanted into the heart was patented in 1960 and soon went into production. Life-saving descendants of this first device now improve the lives of over half a million patients with slow heartbeats every year.



Stomach ulcers

In the 1980s, two Australian doctors were ridiculed for suggesting that stomach ulcers were caused not by business lunches and stress, but by infection with a common bacteria. Barry Marshall, a gastroenterologist and his pathologist colleague in Perth, Robin Warren, noticed that stomach biopsies taken from their ulcer patients all contained the same spiral-shaped bacteria, called Helicobacter pylori.



To prove their hunch, Marshall deliberately downed a pint of foaming helicobacter broth that he’d grown in his lab after isolating it from the stomach of one of his patients. Within a week, he had rampant stomach inflammation – which was then completely reversed by taking antibiotics.



Their discovery has also meant the virtual eradication of a type of stomach cancer caused by helicobacter infection.



For their work (and presumably Marshall’s bravery), Marshall and Warren were awarded the 2005 Nobel prize for medicine.



Antidepressants

Several classes of antidepressants owe their discovery to chance, from iproniazid, which was initially used to treat tuberculosis in the 1950s, to the tricyclics of the 1960s, which stemmed from an experimental treatment for schizophrenia and the more recent breakthrough involving the use of ketamine.

Valium

The entry-level benzodiazapine was developed in the 1950s by a Polish immigrant in the US, Leo Sternbach, from discarded chemical compounds he had synthesised 20 years earlier in Poland when he was working on experiments to create new dyes.

The dyes were a failure. The benzodiazapines quickly became the most popular prescription drugs in the US.