The drug that replaced adrenaline as the Federation's usual remedy for radiation poisoning, introduced in The Deadly Years and still prescribed in the 24th century.
Hyronalin is the standard medicine given to people exposed to harmful radiation. It superseded older treatments so completely that earlier research into them was largely forgotten.
That history matters in the Original Series episode The Deadly Years. After a landing party on Gamma Hydra IV begins ageing by decades in a matter of days, hyronalin proves useless against the unusual radiation involved. Spock and McCoy work out that Chekov was spared because he had been badly frightened, and that adrenaline, the remedy hyronalin had replaced, is the cure.
The drug remains in service long afterwards. In The Next Generation episode Final Mission, Crusher uses it to protect the crew while the Enterprise-D tows a dangerously radioactive barge, and it is mentioned again in Deep Space Nine and Voyager.