[5] In rats, IAA is a product of both endogenous and colonic microbial metabolism from dietary tryptophan along with tryptophol.

On a larger scale, IAA serves as signaling molecule necessary for development of plant organs and coordination of growth.

[14] IAA production is widespread among environmental bacteria that inhabit soils, waters, but also plant and animal hosts.

Distribution and substrate specificity of the involved enzymes suggests these pathways play a role beyond plant-microbe interactions.

A fungus specific to spruce called Tricholoma vaccinum was shown to produce IAA from tryptophan and excrete it from its hyphae.

[17] Research into IAA-producing fungi to promote plant growth and protection in sustainable agriculture is underway.

[23] William Gladstone Tempelman studied substances for growth promotion at Imperial Chemical Industries Ltd. After 7 years of research he changed the direction of his study to try the same substances at high concentrations in order to stop plant growth.

[25] When sprayed on broad-leaf dicot plants, they induce rapid, uncontrolled growth, eventually killing them.

IAA is listed in its MSDS as mutagenic to mammalian somatic cells, and possibly carcinogenic based on animal data.

The NFPA 704 health hazard rating for IAA is 2, which denotes a risk of temporary incapacitation with intense or prolonged, but not chronic exposure, and a possibility of residual injury.

[30] Humans typically have relatively high levels of IAA in their serum (~1 μM), but this can be increased further in certain disease conditions and can be a poor prognostic marker for cardiovascular health.

[35] In 2010 in vitro experiments proved this concept of IAA as an immunotoxin when used in preclinical studies of targeted cancer therapy, as it induced apoptosis in bladder[34] and in hematological malignancies.