Lactobacillus acidophilus is one type of “friendly” bacteria that normally lives in the small intestine, where it produces vitamin K and fights off harmful bacteria 124. Acidophilus is used to treat diarrhea and other digestive ailments as well as vaginal infections, though the effectiveness of these uses is unproven. Acidophilus causes few side effects, but it may pose risks for people with certain health conditions. Talk to your doctor before taking acidophilus.

Infection Risks

Acidophilus products may contain live bacteria, which could grow too much and cause an infection in people who have a weakened immune system. Though the risk is small, some people have developed a serious infection of a heart valve in this way, according to MayoClinic.com. If you have HIV/AIDS or another disease that impairs your immune system, are undergoing treatment for cancer, or have had an organ transplant and are taking medication to prevent rejection, you may be at risk. People with artificial heart valves, short bowel syndrome, intestinal damage or recent bowel surgery may also be more likely to develop an infection from taking acidophilus. If you have any of these conditions, do not take acidophilus without talking to your doctor first.

Side Effects

Acidophilus seems to cause few side effects and they usually involve digestive complaints. Gas, bloating, diarrhea, indigestion and abdominal pain are the most common side effects. These complaints may be reduced if you continue using acidophilus or cut back on the dose, according to MayoClinic.com 1. Some women who have used acidophilus tablets to treat vaginal infections may have burning in the vagina.

Interactions

A number of common medications can suppress the immune system and might increase the risk of infection if you are taking acidophilus, according to MedlinePlus 2. Talk to your doctor of pharmacist before taking acidophilus if you are taking corticosteroids, prednisone, azathioprine, basiliximab, cyclosporine, daclizumab, muromonab-CD3, mycophenolate, tacrolimus and sirolimus. If you are taking antibiotics, which kill off bacteria, they may reduce the effectiveness of acidophilus because it is a form of bacteria. Acidophilus may also interact with sulfasalazine, a drug used to treat ulcerative colitis.

Quality Problems

Be sure to purchase acidophilus from a reliable source because there are questions about the quality of some products. Some acidophilus products contain no acidophilus at all while others have been contaminated with potentially harmful bacteria, according to MedlinePlus 2. In addition, if a product has been sitting on a shelf for a long time, the acidophilus bacteria may die off, which would render the product ineffective.