The saponins, tannins and anthraquinones have been shown to be toxic for microorganisms and to suppress methane production in animal nutrition researches and also in a recent study on the waste treatment achieved by Mambanzulua et al.. However, to our knowledge, few works are published on the evaluation of methanogenic inhibition process by PSMs in anaerobic digestion processes treating wastes. Consequently, there is a lack of information about the toxic effects and about potential inhibition. Some publications about non glycosylated phenolic monomers are focused on the evaluation of the inhibitory effects of aromatic structure on methanogenesis. There are also some inconsistencies about methane inhibition in for instance studies on saponins. Besides, the information available on methanogenic fermentation of phenolic compounds is fragmented and sometimes contradictory. It also lacks a consistent use of units for reporting biomass concentration. That does not allow compare the anaerobic degradation of these compounds.