Journal of Advances in Medical and Pharmaceutical Sciences

Trimethylamine N-oxide (TMAO) is a dietary metabolite at the intersection of microbiota metabolism and host response. Chronically elevated TMAO has been associated with negative outcomes in cardiovascular, renal, and neurological disease and, at physiological levels, appears to support protein homeostasis as an osmolyte. In this review, we integrate findings from along the gut–liver–kidney–brain axis, where available, and differentiate preclinical mechanisms from clinical associations to help contextualize and prevent overinterpretation as causality. Dietary precursors are metabolized to trimethylamine by gut microbiota, followed by oxidation to TMAO by hepatic flavin-containing monooxygenase-3 (FMO3) and absorption. Elevated circulating TMAO has been linked to endothelial dysfunction, inflammation, and prothrombotic signaling. We discuss the circumstances under which TMAO may be protective or pathogenic and strategies to mitigate the harmful effects without disrupting its physiological functions. Precision interventions to target TMAO pathways are emerging as promising and achievable approaches to risk reduction, including dietary manipulation, inhibition of microbial TMA-lyase activity, and modulation of hepatic FMO3 activity. We outline future research directions by focusing on setting tissue-specific thresholds for TMAO's homeostatic and pathogenic roles and incorporating causal inference criteria into microbiome–host interaction studies to enable strategy development.