Streptococcus salivarius K12

Safety profile

Across 4 clinical studies, there were no reports of increased adverse events with Streptococcus salivarius K12 compared to control. In two studies, specific safety markers (blood clinical chemistry and hematology) showed no significant differences between groups, and the probiotic was described as well tolerated in three studies. Notably, two findings from one study indicated statistically significant reductions in upper respiratory infections and acute otitis media, which are beneficial effects rather than adverse events.

Caveats: Most studies were likely short-term and focused on efficacy in healthy populations; long-term safety and safety in vulnerable groups (e.g., children, immunocompromised individuals) are not well characterized. The evidence base is small (4 studies), and absence of reported adverse events does not establish safety.