Product of intermediary Metabolism released from a cell, such as an antibiotic.

Secondary metabolites are those chemical compounds in organisms that are not directly involved in the normal growth, development or reproduction of organisms. Typically primary metabolites are found across all species within broad phylogenetic groupings, and are produced using the same pathway (or nearly the same pathway) in all these species. Secondary metabolites, by contrast, are often species-specific (or found in only a small set of species in a narrow phylogenetic group), and without these compounds the organism suffers from only a mild impairment, lowered survivability/fecundity, aesthetic differences, or else no change in phenotype at all, especially when observed in controlled and optimized laboratory conditions.