Written by Poul Anderson
Copyright 1960
First appearing in Fantastic Stories of Imagination, Dec 1960. Hearing of yet another unknown human planet in the Betelgeuse System, Dominic Flandry heads to investigate and finds a planet whose air is filled with poisonous bacteria. The residents must take a pill provided by a company called Biocontrol and that company wants to keep it that way. Contained in the collection Flandry of Terra.
Here are the pages I have of it.