Penicillin was discovered in 1928 by Scottish bacteriologist Alexander Fleming at St. Mary’s Hospital in London.

Quick Scoop: What “invented” means here

People often ask “when was penicillin invented,” but strictly speaking it was discovered , not invented, because it is a natural substance made by a Penicillium mould. Fleming noticed that a contaminating mould on one of his bacterial culture plates was killing the surrounding bacteria and named the antibacterial substance “penicillin” in 1928.

From discovery to usable drug

Turning that lucky lab discovery into a medicine took more than a decade.

  • 1928: Fleming observes the mould and identifies the substance as penicillin.
  • 1930: Fleming’s student Cecil George Paine first uses crude penicillin to successfully treat an eye infection in a newborn.
  • 1939–1940: A team at Oxford led by Howard Florey and Ernst Chain purifies penicillin and proves in animal tests that it can fight serious infections.
  • Early 1940s: Large‑scale production ramps up (with major help from the United States), and penicillin becomes the first widely used antibiotic.

So if you just want the date: penicillin was discovered in 1928, and it became a practical, mass‑produced drug in the early 1940s.

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