Probiotics: Benefits, Side Effects, Dosage, and Interactions

Probiotics are live bacteria and yeast that are good for you, especially your digestive tract. These naturally occurring microorganisms are considered "good" in that they keep "bad" bacteria and fungus in check. They can even promote vaginal health by preventing the overgrowth of microbes that cause yeast infections and bacterial vaginosis.

Probiotics are found in yogurt and fermented foods but can also be purchased as dietary supplements, skin care products, and vaginal suppositories.

The most common types of probiotics sold in the United States are Lactobacillus and Bifidobacterium. The increasing popularity of these products has led to misconceptions about what they can and cannot do and whether they can deliver the promised results.

Health Benefits

A lot of research has been devoted to evaluating the benefits of probiotics, most especially in the area of digestive health. While some of the results have been positive, other long-held health claims have been unsupported by research.

Here are some of the key findings from recent research:

Irritable Bowel Syndrome

One area of research has been centered on whether probiotics are helpful in managing the symptoms of irritable bowel syndrome (IBS). Many of the studies have looked into whether specific probiotic strains (or combination of strains) are effective in alleviating the abdominal pain, bloating, diarrhea, or constipation common with IBS.

A 2010 review of studies from Georgetown Univerity concluded that probiotics in general were likely beneficial to the treatment of IBS but that one specific strain—Bifidobacterium infantis—has emerged as a frontrunner for treatment.

A 2011 expert consensus from both the United States and Europe echoes these conclusions, stating that there is "reasonable rationale" support the use of probiotics as an adjunctive (supportive) therapy for IBS.

Antibiotic-Associated Diarrhea

Other studies have focused on whether probiotics can play a role in preventing diarrhea caused by antibiotic use. Since antibiotics can kill both "good" and "bad" bacteria, the hope has been that probiotic supplements could help restore the digestive flora back to its normal state. The results to date have been mixed.

A 2016 study in the American Journal of Infection Control reported that from 2006 to 2012, 96 percent of the 145 hospitals studied in the United States gave probiotics to their patients in hopes of preventing antibiotic-associated diarrhea. In evaluating outcomes, the researchers found that probiotics were no more effective than a placebo.

Other studies have come to opposite conclusions, asserting that certain strains of probiotic bacteria are simply better than others.

A 2018 review of studies from China concluded that probiotics can reduce the risk of diarrhea by 50 to 60 percent if taken with antibiotics, particularly the probiotics Saccharomyces boulardii and Lactobacillus rhamnosus GG.

Vaginal Infections

The use of probiotics in treating common vaginal infections, like bacterial vaginosis and vaginal candidiasis (yeast infection), remains controversial with some studies showing benefits and others not.

A 2014 review in the Journal of Lower Genitourinary Tract Disease would only go so far as to say that oral probiotics taken daily may prevent the recurrence of bacterial vaginosis but would unlikely offer much in the way of treatment.

Of the oral supplements reviewed, Lactobacillus acidophilus, Lactobacillus rhamnosus GR-1, and Lactobacillus fermentum RC-14 were considered the most beneficial.

By contrast, the oral or vaginal use of probiotics has not yielded positive results in treating yeast infections, according to a 2006 review in the Journal of Antimicrobial Chemotherapy.

Inflammatory Bowel Disease

Inflammatory bowel disease (IBD), which consists of ulcerative colitis and Crohn's disease, is characterized by persistent gastrointestinal symptoms, including abdominal pain, bloating, blood in stool, flatulence, diarrhea, nausea, and vomiting.

Interestingly, while much of the current evidence suggests that probiotics that may prevent recurrence of ulcerative colitis (arguably the more serious of the two conditions), the same was not seen with Crohn's disease. Moreover, the benefits were attributed to specific probiotic strains or combinations of strains.

In 2011, VSL#3 (a high-potency combination probiotic) and the probiotic Escherichia coli Nissle 1017 were both given an A rating at the 3rd Yale Workshop on Probiotics based on strong evidence that they sustained remission of ulcerative colitis.

By contrast, a 2009 Cochrane review, which evaluated 23 different randomized controlled studies, found that probiotics were no more effective in preventing or treating Crohn's disease than a placebo.

Possible Side Effects

Probiotic supplements are considered safe and well-tolerated if taken as directed. Side effects may include bloating and gas. Taking a yeast-based probiotic can sometimes cause constipation or increased thirst. Most of these side effects are mild and tend to improve once your body adapts to treatment.

Probiotics may contain allergens that can affect people with an egg or soy allergy. People with a yeast allergy would need to avoid yeast-based probiotics.

There are no documented drug interactions associated with probiotic supplements. With that said, speak with your doctor before taking a probiotic if you are on antibiotics or antifungal medications. Taking these together can negatively alter your digestive or vaginal flora.

Dosage and Preparation

Because there are many different probiotic strains and formulations, there is no set dosage. Factors like age, weight, and general health may influence how much or little you need.

As a general rule, a probiotic should provide at least 1 billion colony forming units (CFU) per day, with dosages ranging from 1 billion to 10 billion for adults. If used in children, less than 1 billion CFU would be prescribed. Probiotic supplements are generally taken on a daily basis, ideally before a meal.

Probiotic suppositories tend to have higher CFUs as they are meant for short-term use only. Generally speaking, suppositories should be used for no more than seven consecutive days.

What to Look For

In the United States, probiotics are classified as dietary supplements. Under this classification, the products are not strictly regulated and are allowed to be sold without the burden of clinical research. With that being said, the U.S. Food and Drug Administration (FDA) forbids manufacturers making any claims that the products can cure, treat, or prevent any disease or health condition.

To ensure quality and safety, only buy supplements that have tested and certified by an independent certifying body like the U.S. Pharmacopeia, ConsumerLab, or NSF International.

When used as a food ingredient, probiotics fall under the FDA umbrella category "GRAS," meaning they are "generally regarded as safe."

Health Benefits of Probiotics

Can a daily supplement treat IBS, diarrhea, and yeast infections?