nonpathogen
A carcinogen is an agent that causes cancer.
pathogenAn agent of infection is a pathogen.
Something that is cancer-causing is carcinogenic.
A cytotoxin is an agent that kills cells
In medical terms, an agent usually refers to a medication. For instance, an antihypertensive agent reduces blood pressure.
A teratogen is an agent that causes birth defects.
An antimotility agent controls loose stools.
An antineoplastic agent is one that works against tumors. A tumor is also known in medical terms as a neoplasm.
Antagonist is a process or agent that works against another.
The word you're searching for is "etiology", as in; "The patient presented complaining of severe lower back pain, etiology unknown."Etiology means cause of an illness.
bronchodilators
An agent used to increase the effectiveness of a medication is a "potentiator".An agent used to increase the effectiveness of a medication is a "potentiator".