I often hear “nauseous” on TV where “nauseated” would be correct.

Problem:
“Nauseous” and “nauseated” traditionally are not synonyms.

Explanation:
“Nauseous” traditionally has meant causing nausea. For example, a nauseous smell refer to a smell that induces nausea. The traditional distinction between “nauseous” and “nauseated” is worth keeping, in my opinion. A nauseous man should not mean the same as a nauseated man.

Solution:
Use “nauseous” — or “nauseating” — when you want to indicate causing nausea; use “nauseated” otherwise.