Gut Microbes May Decide Whether Your Medicine Works or Harms You

A new review in Discover Pharmaceutical Sciences argues that gut microbes may help explain why the same drug, at the same dose, can work for one patient and fail or even harm another. The paper describes pharmacomicrobiomics, a field studying how differences in the human microbiome affect drug absorption, distribution, metabolism, excretion, efficacy, and toxicity. The authors frame gut microbiota as a dynamic “second genome” that complements rather than replaces pharmacogenomics. They describe multiple mechanisms, including microbial enzymes that transform drugs and influence liver and intestinal pathways, plus bioaccumulation inside bacterial cells that can reduce systemic absorption. The review also highlights clinical examples such as irinotecan’s activation.