Friendly bacteria for the digestive system! Acidophilus (Lactobacillus acidophilus ) is a group of “friendly” bacteria that normally lives in the human small intestines. Natrol® Acidophilus is a probiotic that provides healthy bacteria to promote digestive health and helps maintain a healthy intestinal tract. Probiotics, such as Acidophilus, are friendly bacteria that colonize the human digestive tract and promote digestion and good gastrointestinal health.