“The human gut harbors trillions of invisible microbial inhabitants, referred to as the microbiota, that collectively produce thousands of unique small molecules. The sources and biological functions of the vast majority of these molecules are unknown. Yale researchers recently applied a new technology to uncover microbiota-derived chemicals that affect human physiology, revealing a complex network of interactions with potentially broad-reaching impacts on human health.”
The 2019 paper in the journal Cell from which the above quote is taken is : A Forward Chemical Genetic Screen Reveals Gut Microbiota Metabolites That Modulate Host Physiology
“The human gut microbiota produces thousands of unique small molecules that can potentially affect nearly all aspects of human physiology, from regulating immunity in the gut to shaping mood and behavior”
Since the human gut microbiome is extremely variable from one individual to another - and even within the same individual over time - it make prove an almost impossible task to investigate and document possible chemical interactions.
Note: The numbers for the size of a 'normal' human gut microbiome (i.e. the number of microorganisms present) are currently disputed. Estimates vary from 10X the number of cells in the human body down to 3X (ref. needed)