Med alert was an emergency alert used to contain people with contractible illnesses.

In 2364, Captain Jean-Luc Picard ordered a med alert on the USS Enterprise-D to Dr. Beverly Crusher, after T'Jon and Romas told him that there was a plague on their homeworld, Ornara. It was later revealed that the Ornarans were all addicted to the drug felicium and had run out of it, causing severe withdrawal pains. (TNG: "Symbiosis")