1920 - 1930

1922
The UK Institution of Chemical Engineers (IChemE) is founded.
Medicines commonly used by the late 1920s include aspirin, codeine, and morphine for pain; digitalis, nitroglycerin, and quinine for heart disorders, and insulin for diabetes. Other drugs included antitoxins, a few biological vaccines, and a few synthetic drugs.

In the 1930s antibiotics emerge:
first sulfa drugs, then penicillin and other antibiotics.
In the 1950s other drugs emerge including corticosteroids for inflammation, rauwolfia alkloids as tranqulizers and antihypertensives, antihistamines for nasal allergies, xanthines for asthma, and typical antipsychotics for psychosis. As of 2008, thousands of approved drugs have been developed. Increasingly, biotechnology is used to discover biopharmaceuticals.
https://en.wikipedia.org/wiki/Institution_of_Chemical_Engineers

1925
The use of poison gas, including mustard gas, during warfare, a practice known as chemical warfare, is prohibited by the Geneva Protocol
https://en.wikipedia.org/wiki/Geneva_Protocol