Acidophilus is also called lactobacillus acidophilus. Lactobacillus acidophilus is a bacteria that exists naturally and primarily in the intestines and the vagina. Acidophilus can prevent the growth of harmful bacteria. Long-term use of lactobacillus acidophilus should be safe.
Also, you may want to eat fresh foods which are beneficial to your intestinal health and general health and avoid any foods that have given you diarrea.