Homovanillic acid is a monocarboxylic acid that is the 3-O-methyl ether of (3,4-dihydroxyphenyl)acetic acid. It is a catecholamine metabolite. It has a role as a mouse metabolite and a human metabolite. It is a member of guaiacols and a monocarboxylic acid. It is functionally related to a (3,4-dihydroxyphenyl)acetic acid. It is a conjugate acid of a homovanillate. Homovanillic acid is used as a reagent to detect oxidative enzymes, and is associated with dopamine levels in the brain. Abnormalities in white matter were associated with low CSF Homovanillic acid.

Ganoderic acid T-Q and TR are two inhibitors of H5N1 and H1N1 NAs.