3 bm dark green what could cause it?

Green Stool: The most common ingested causes of black stool would be iron supplements, licorice, and peptobismol. Bleeding in the GI tract can also lead to dark stool. Green comes most commonly from bile in the GI tract.

Normal: The stool color is provided by the bile from the liver that is adds to fecal debris.It starts out a deep green & slowly changes thru greens to yellows to browns as the germs in the intestines metabolize the bile.Green generally means the stool in question moved through faster or was subject to less change by gut germs.If worried about something else schedule a visit.