**2. Mechanisms of enteral damage**

Enteral damage and consequent symptoms such as diarrhea, bloating, flatulence and pain may be mediated through different mechanisms falling into two main categories: (1) Functional damage: it can be caused by abnormalities in any of the mechanisms involving digestion (maldigestion) and/or absorption (malabsorption), GI motility disturbances, alterations in the water and electrolyte absorption and/or secretion mechanisms, and altered microbiota and/or microbiome (dysbiosis), and (2) Microscopic or overt mucosal damage: this can be caused by direct contact of the drug, ischemic-related damage, systemic inflammatory or autoimmune mechanisms, and may affect different portions of the small intestine, colon, or both (**Figure 1**, [9]). According to the involved mechanism, main symptoms may predominate diarrhea, malabsorptive complaints such as steatorrhea, weight loss and anemia, or abdominal pain, and in severe cases, occult or overt bleeding.
