Nonhormones

Nonhormones is a term used in biology and pharmacology to describe substances that influence physiological processes but are not classified as hormones themselves. The usage of the term varies by field, and it is not a strict scientific category. In general, nonhormones can include local signaling mediators, neurotransmitters, pharmaceutical agents, and environmental chemicals that affect endocrine function without acting as circulating endocrine hormones.

A key distinction is that classical hormones are secreted by endocrine glands and travel through the bloodstream to distant targets. Nonhormones, by contrast, often exert effects locally (paracrine or autocrine signaling) or modulate hormone action indirectly. They may influence hormone synthesis, release, receptor expression, or downstream signaling pathways without being hormones in the strict sense.

Examples of nonhormonal signaling molecules include prostaglandins and nitric oxide, which regulate inflammation, vascular tone, and other processes without acting as systemic hormones. In medicine and pharmacology, many drugs influence hormone systems without themselves being hormones—for instance, drugs that alter hormone synthesis, metabolism, or receptor activity.

The concept also intersects with environmental health, where chemicals that disrupt hormonal systems but are not hormones themselves are discussed as nonhormonal disruptors or endocrine-disrupting chemicals. Because the boundary between hormones and nonhormones is not rigid, the term is most useful as a descriptive label rather than a formal classification.