Summarize this article:

The major effect of nearly all probiotics is to improve your gut and digestive health (in addition to whatever other benefits the bacteria provide). If you've been using a certain probiotic supplement for a couple of weeks and don't notice an improvement in your digestive health, it's time to try a new probiotic. Signs of an ineffective probiotic include: Stomach cramps. Intestinal pain. Constipation or diarrhea. Keep in mind that, since most probiotics are sold as dietary supplements, they aren't guaranteed to produce the results they advertise. Fortunately, another probiotic may fix your health concern. If the first probiotic you tried isn't helping, switch to another type. Unlike medication, you can change your probiotic supplement without experiencing major side-effects. The only side-effect you're somewhat likely to experience as a result of switching is mildly upset stomach. Most medical studies on probiotics have been performed on strains of Lactobacillus and Bifidobacterium. Probiotics containing these strains are most likely to match the claims made on the label. Choose well-known strains of these bacteria to help with common health ailments. These include: Lactobacillus bulgaricus, which helps with lactose intolerance and various resultant digestive problems. Lactobacillus reuteri LR-1 or LR-2, which improves dental hygiene and prevents tooth plaque from forming. Bifidobacterium infantis 35624 or MIMBb75, which decreases bloating and discomfort from IBS. If you have frequent moderate to severe abdominal pain, or chronic constipation or diarrhea, the problem may be more severe than a probiotic can handle. Talk to your physician and explain your condition to them. Also ask your doctor if they recommend any specific probiotics or know of any to avoid. You may be suffering from an undiagnosed case of IBS, or you may be lactose intolerant or have Celiac disease without knowing it.

Summary:
Pay attention to your body's digestion. Revise your probiotic supplement as needed. Choose studied strains of probiotic to help with frequent health concerns. Talk to your doctor if you're concerned about your digestion.