Is it possible to put alka seltzer cold and cough in a humidifier?

No: If want to active ingredients in alka seltzer to enter your body, using a humidifier will prevent this from happening. The medicine will not vaporize efficiently; it will be trapped in the humidifier itself.

No: Not a good idea...But a good question. The particles are too big. It is meant to go through the digestive tract and not immediately to the respiratory tract.