Green stool — when your feces (poop) looks green — is usually the result of something you ate, such as spinach. Green stool also can occur after you consume certain medications or iron supplements.
Newborns pass a dark green stool called meconium and breast-fed infants often produce yellow-green stools. In older children and adults, green stool is uncommon and rarely cause for concern.
Green stool
Causes shown here are commonly associated with this symptom. Work with your doctor or other health care professional for an accurate diagnosis.
Source: mayoclinic.org