Is VSL3 Safe?

Clinical studies have shown that VSL3 probiotics can be taken safely for long periods of time without any problems. Adjustment of the intestinal flora after VSL3 administration can take a few days or weeks and it can take up to a month for the colonization of the gut to become optimally stable.


Probiotics, including the strains in VSL#3®, have a long history of safe use in foods34. The safety of VSL#3® is well established by the substantial historical use of the contained microorganisms in fermented dairy products35,36. Many probiotic species are integral to the production of fermented foods and have been consumed safely as part of these foods for millennia15. Furthermore, many bifidobacteria and lactobacilli species are normal, nonpathogenic inhabitants of the human gastrointestinal tract, oral cavity, skin, and vagina15,37-39. While theoretically probiotic species could act as opportunistic pathogens, epidemiological surveillance data indicate that the risk of infection from consumption of lactobacilli is negligible35,40. In the available literature, documented cases of infection attributable to probiotic treatment are rare and limited to case reports. These case reports are primarily associated with patients having compromised immune systems or other major health problems41-45. Each strain of probiotic bacteria in VSL#3® is both non-pathogenic and non-toxigenic. The use of these particular strains in VSL#3® medical foods has been confirmed as generally recognized as safe (GRAS)56 for use in foods. The lactic acid bacteria in VSL#3® have a long history of use in foods. Studies of VSL#3® have been conducted in several animal models of colitis and inflammatory liver disease46-51, 56. In experimental animal models of colitis, there are serious derangements in epithelial permeability and barrier function, causing the animals to be particularly vulnerable to bacterial translocation. These studies demonstrate that VSL#3® normalizes gut permeability and barrier function52-54. Thus, despite increased gut permeability and inadequate barrier function the probiotics contained within VSL#3® do not translocate from the gut lumen and act opportunistically when ingested by animals with colitis.

VSL#3® products are manufactured in accordance with Current Good Manufacturing Practice for foods, using ingredients that are listed by the U.S. Food and Drug Administration (FDA) as food or food additives, or are “Generally Recognized as Safe” (GRAS)56 food substances. The lactic acid bacteria in VSL#3® have a long history of use in foods15,34.

Allergen Status

All formulations of VSL#3® contain none of the following: wheat, gluten (other cereals), soy, milk (including lactose), crustacean shellfish, eggs, peanuts, nuts, fish, celery, mustard, sesame seeds, sulfur dioxide and sulfites (>10 mg/kg), lupin, mollusks. VSL#3® contains cornstarch, an inactive ingredient, which is generally well-tolerated.
GMO Status All formulations of VSL#3® do not consist of, nor contain, nor are produced from genetically modified organisms according to the definitions of Regulation (EC) 1829/2003 and Regulation (EC) 1830/2003 of the European Parliament and the Council of 22 September 2003.

All formulations of VSL#3® are Kosher and Halal-certified.

Interactions with other medications

VSL#3® is believed to be compatible with most types of drugs. If taken with antibiotics, VSL#3® should be consumed in-between antibiotic doses thereby maximizing the probiotic effect.

Side Effects

Mild abdominal bloating has been reported in the first few days of consuming VSL#3®. This is usually a transitory phenomenon due to the changing intestinal microflora. If you experience bloating, you may need to reduce your daily  intake to allow for this adjustment.