3-Indolepropionic acid (IPA), or indole-3-propionic acid, is a potent neuroprotective antioxidant and plant auxin that is being studied for therapeutic use in Alzheimer's disease. It is endogenously produced by human microbiota and has only been detected in vivo when the species Clostridium sporogenes is present in the gastrointestinal tract. As of April 2016, C. sporogenes, which uses tryptophan to synthesize indole and subsequently IPA, is the only species of bacteria known to synthesize IPA in vivo at levels which are subsequently detectable in the blood plasma of the host.