How to Choose a Probiotic

Among the dizzying array of choices, some probiotics seem to be effective for certain conditions, while others have no effect at all. Here’s how to tell the difference.

Probiotics may help a startlingly long list of conditions, studies suggest: acne, weight loss, and behavioral and neurological disorders such as Alzheimer’s, ADHD, and autism are just a few. Even the common cold — perhaps particularly in children — makes the list.

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As the number of studies grows, so do the brands and supplements on the market. If you’re interested in taking a probiotic, how do you choose among them? 

It’s a complicated question. Not only is there a dizzying array of choices, but some probiotics seem to be effective for certain conditions, while others have no effect at all. The friendly bacteria in probiotics come from yeast or lactic acid bacteria, of which there are many strains: two of the most common are Lactobacillus and Bifidobacterium. Scientists are still working out the various strains and their effects — and much of their research is preliminary.

Yet studies demonstrating benefit in people have been appearing for years. Below, we explore some of the most promising. Note that probiotics are classified according to genus, species, and strain. While strain details — indicated by letters or numbers — are not always provided in clinical studies, we give them here (in parentheses) when possible.

Diarrhea and IBS. Perhaps the strongest evidence for probiotics comes in cases of digestive upset. For such complaints, consider Saccharomyces boulardii (though see warnings regarding this strain below). One review gave cautious support for its effectiveness in a number of digestive conditions, from Crohn’s disease to irritable bowel syndrome (IBS); another strongly recommended it for traveler’s and antibiotics-associated diarrhea. Other probiotic strains may be effective, too. In a 2007 trial, a cocktail of Lactobacillus casei (DN-114001), Streptococcus thermophilus, and Lactobacillus bulgaricus reduced diarrhea in adults over 50 taking a course of antibiotics by nearly two-thirds. Meanwhile, the effects of probiotics for IBS tend to vary from study to study, but most show some benefit: if one doesn’t work for you, try another.

Depression. Look for Lactobacillus helveticus (R0052) and Bifidobacterium longum (R0175), which were shown to decrease depression and other negative feelings while improving ability to cope in a small trial in people. Other strains have shown promise. In a recent study, human participants taking a product called Ecologic Sense — a cocktail of Bifidobacterium (bifidum W23 and lactis W52), Lactobacillus (acidophilus W37, brevis W63, casei W56, and salivarius W24), and Lactococcus lactis (W19 and W58) — had reduced reactivity to sad moods at the end of four weeks. 

Lowering cholesterol. In trials, a combination of Lactobacillus acidophilus and Bifidobacterium bifidum moderately decreased total and LDL cholesterol in adults, while children with high cholesterol also benefited from a combination of Bifidobacterium animalis subspecies lactis (MB 2409), Bifidobacterium bifidum (MB 109B), and Bifidobacterium longum subspecies longum (BL04).

Vaginal health. A combination of Lactobacillus rhamnosus (GR-1) and Lactobacillus reuteri (RC-14) healed bacterial vaginosis in 87.5 percent of women in one small 2008 trial. (Two products contain this combination, the independent testing group ConsumerLab points out — RepHresh Pro-B and Jarrow Women’s Fem Dophilus — but Jarrow’s version costs half as much.) There is also evidence probiotics help with yeast infections: one pilot trial testing vaginal application of Lactobacillus fermentum LF10 (DSM 19187) and Lactobacillus acidophilus LA02 (DSM 21717), available in a product sold in Europe, also saw high success rates.

If you’re interested in trying probiotics for a specific condition, start by verifying the strains used in studies. Taking a probiotic with multiple strains might maximize effects, yet the single strains in Align (Bifidobacterium infantis 35624), Culturelle (Lactobacillus GG), and Cardioviva (Lactobacillus reuteri NCIMB 30242) also have demonstrated benefits for a variety of conditions. The best option may be to start simply, with a single strain matched to your condition. 

Then, take one dose a day or even every other day to start, with food, while evaluating how you feel. For most people, any initial gastrointestinal discomfort (gas or bloating) subsides within a few days. Any benefit should be apparent fairly quickly: if you don’t see improvement after a few weeks, try another strain.

Be sure to shop around. Prices vary widely, from $20 to $30 for a monthly supply to significantly less, and are not always an indicator of quality. Some store-brand probiotics offer one only strain, for example — Lactobacillus acidophilus, which can be found in most yogurts. If you’d like to try it, simply eat plain yogurt labeled as having “live and active cultures” rather than take an expensive supplement. Brands may also vary in quality and contents (for a fee, ConsumerLab offers access to its tests of numerous probiotics). Reputable brands should indicate whether a probiotic needs to be refrigerated and include an expiration date on the bottle.

Adequate dosing is another open question. Most experts agree a supplement should contain at least 1 million colony-forming units, or CFUs, per dose. Packaging claiming a certain number of CFUs at the time of manufacture can be misleading, however, since, transport and storage conditions — particularly heat — can all affect the number of cultures that remain alive by the time a probiotic reaches your home. (While there is some evidence probiotics can be beneficial even after the bacteria they contain have died, effects may be unpredictable; stick with live cultures to be safe.) Look for manufacturers who guarantee CFUs up to the expiration date. Some, ConsumerLab says, deliberately provide more CFUs than claimed on a product’s packaging to account for loss over time.

While the buzz around probiotics is growing, not everyone is jumping on the bandwagon. To date, adverse effects from probiotic treatment are extremely unusual. Probiotics have been studied extensively in children, frequently to treat diarrhea, and studies in pregnant and breastfeeding women report no harmful effects. 

However, there are some cautions. People with a heart or liver condition or a severely weakened immune system — such as infants born prematurely or those taking immunosuppressant drugs — should be very cautious with probiotics, as should anyone using a venous catheter. (These groups should avoid the related strains Saccharomyces cerevisiae and Saccharomyces boulardii, in particular, because they’re associated with bacterial infection.) As with any change in your health, always talk with your healthcare provider before taking a supplement. 

While most researchers suggest there’s no harm in consistent supplementation, they remain wary of recommending it. Aside from questions of dosing and strain, it’s still relatively unclear how probiotics work at all. They may act differently in different people, for example, since intestinal bacteria vary from person to person. “Probiotic supplementation appears to be of therapeutic value,” one review concluded, but “clinical data to date remain controversial.”