histaminergic histaminergic histaminergic means "working on the histamine system", and histaminic means "related to histamine". a histaminergic agent (or drug) is a chemical which functions to directly modulate the histamine system in the body or brain. examples include histamine receptor agonists and histamine receptor antagonists (or antihistamines). subdivisions of histamine antagonists include h1 receptor antagonists, h2 receptor antagonists, and h3 receptor antagonists.