Spores released by pod plants on Omicron Ceti III that live in symbiosis with humanoid hosts, shielding them from deadly Berthold rays while leaving them blissfully content and without ambition.
The spores of Omicron Ceti III are carried by flowering pod plants and drifted to the planet from elsewhere in space. Once inhaled they live within a humanoid host, keeping the body in perfect health and protecting it from the Berthold rays that bathe the planet, which would otherwise kill within weeks.
They appear in the Original Series episode This Side of Paradise. The colonists led by Elias Sandoval have survived for three years thanks to the spores, but have achieved nothing in that time. Leila Kalomi exposes Spock, who for once feels happiness, and almost the entire Enterprise crew beams down to join the colony.
Kirk discovers that violent emotion drives the spores out. He goads Spock into a rage, and the two then use a subsonic signal to provoke quarrels on the surface and free everyone.