The Dude Abides said...
A few years ago, there was at least one thread by a (now former) forum member about how Saccharomyces Boulardii negatively affected them. I recall the user, but not the exact details around their issue. Since then, most of their posts have been deleted. However, I'm pretty sure it had to do with S. Boulardii being a yeast.
While the details escape me, their report left me wary of the compound. Now, I wouldn't necessarily take or avoid any medication or supplement based solely on one anecdotal report. I'd want to look for additional evidence, though multiple user anecdotes aren't totally worthless.
Anyway, this thread got me thinking about Saccharomyces Boulardii again, due to my own gut issues that have been especially bothing me over the past two years.
S. Boulardii was first isolated just over 100 years ago.
Saccharomyces boulardii is a tropical yeast first isolated from lychee and mangosteen fruit peel in 1923 by French scientist Henri Boulard. Although early reports claimed distinct taxonomic, metabolic, and genetic properties, S. boulardii is genetically a grouping of S. cerevisiae (a species of yeast we know as brewer's yeast or baker's yeast) strains, sharing >99% genomic relatedness, giving the synonym S. cerevisiae var. boulardii.
S. boulardii is sometimes used as a probiotic with the purpose of introducing beneficial microbes into the large and small intestines and conferring protection against pathogens. It grows at 37 °C (98.6 °F). In addition, the popular genome-editing tool CRISPR-Cas9 was proven to be effective in S. boulardii. Boulard first isolated this yeast after he observed natives of Southeast Asia chewing on the skin of lychee and mangosteen in an attempt to control the symptoms of cholera. In healthy patients, S. boulardii has been shown to be nonpathogenic and nonsystemic (it remains in the gastrointestinal tract rather than spreading elsewhere in the body).
It's remarkable what's happened, both good and not so good, over the past 100 years.
I think problems with SB are rare and mainly in severely immunocompromised people as noted below. I've taken SB for at least a few years with no noted problems.
https://www.ncbi.nlm.nih.gov/pmc/articles/pmc3316799/