Penicillin

Penicillin was a medicine discovered on Earth by Alexander Fleming.

In 2008, Plummer of the Pharm said that once they'd developed Reset for human use, it would be bigger than penicillin. (TW: Reset)

In an alternative timeline, Eric Charles Vincent murdered Fleming in December 1927, some months before he would have discovered penicillin. Without it, Earth was ravaged by meningitis and pneumonia in 1956. (BFA: The Sirens of Time)