A reader asked me about this probiotic and I thought that I should dig into it as it is often in probiotic mixtures.
Wikipedia gives a great summary with two items of note:
- “In healthy patients, S. boulardii has been shown to be nonpathogenic and nonsystemic”
- “in immunocompromised individuals, S. boulardii has been associated with fungemia or localized infection, which may be fatal.”
Oh…. we just hit a clear issue of safety for CFS patients (or anyone else with a chronic condition) — it’s safety is unknown. We have the classic over simplification happening here — “Yes, studies show that it is good for you (IF YOU ARE A HEALTHY INDIVIDUAL)”. Studies on CFS/IBS/FM patients are really required.
More quick notes from Wikipedia:
- IBS: improved in one study. No effect in another.
- Decreases E.Coli (which CFS patients are low in) — not good
What else do we know?
- No studies with fibromyalgia
- No studies with chronic fatigue syndrome
- 4 Studies with Irritable Bowel Syndrome (ONLY with diarrhea-dominant version)
- “The improvement of the symptom score was greater with mesalazine alone or combined with Sb as compared with Sb treatment alone.”
- “S.boulardii treatment for 30 days in diarrhea predominant IBS patients did not result in any improvement in this study.” 
- “S. boulardii improved IBS-Quality Of Life better than placebo but was not superior for individual symptoms in patients with diarrhea-predominant IBS or mixed-type IBS.”  – the improvement in the QOL may be a placebo effect.
- “S. boulardii with ispaghula husk was superior to placebo with ispaghula husk in improving the cytokine profile, histology, and quality of life of patients with IBS-D. These preliminary results need to be confirmed in a well-powered trial.” 
- Going to the heavy weight dysfunction, Crohn’s Disease, 11 hits
- Saccharomyces boulardii does not prevent relapse of Crohn‘s disease.
- “S. boulardii added to baseline therapy improved intestinal permeability in these CD patients, even though complete normalization was not achieved.”
- “Clinical relapses as assessed by CDAI values were observed in 37.5% of patients receiving mesalamine alone and in 6.25% of patients in the group treated with mesalamine plus the probiotic agent.”
- “The group treated with S.b. showed a significant reduction in the frequency of bowel movements in the tenth week, to 3.3 +/- 1.2 evacuations per day,” 
There is no clean evidence of any significant improvement with CFS or any related condition, there is also a risk of potentially fatal reaction. Immunocompromised patients and CFS individuals are frequently cited together in studies, additionally, often items used by CFS individuals suppression inflammation and thus part of the immune system. We need more studies (which are expected to show no or marginal results) before this should be included – IMHO.
Do not explicitly take this probiotic.
For items like candida, it is effective but should be used only when needed.
- “Prophylactic S. boulardii supplementation is as effective as nystatin in reducing fungal colonization and invasive fungal infection, more effective in reducing the incidence of clinical sepsis and number of sepsis attacks” 
- “Capric acid secreted by S. boulardii inhibits C. albicans filamentous growth, adhesion and biofilm formation. ”
See this uBiome post it encourages bacteria that inhibit bifidobacteria.