This study scared me away from trying Probiotics:

Probiotics linked to brain fog, severe abdominal bloating

https://www.healio.com/news/gastroenterology/20180808/probio...

“What we now know is that probiotic bacteria have the unique capacity to break down sugar and produce D-lactic acid,” he said in the press release. “So, if you inadvertently colonize your small bowel with probiotic bacteria, then you have set the stage for potentially developing lactic acidosis and brain fogginess.”