Researchers from my alma mater, Boston University, recently looked into just this question. After purchasing several drugstore probiotics, they cracked open the pills, diluted the bacterial powder stuffed inside, and dabbed the mix onto petri dishes to see what would grow. "The numbers from our methods have been a little lower than what's claimed on the box, but there are definitely living bacteria in there."
“A healthy collection of gut bacteria is not one type of bacteria. It’s many types of bacteria, so there could be potential health benefits of having more variety."
Ultimately, the hope is that the research will help doctors and consumers make more informed choices about over-the-counter and food-based probiotics. And while you should always talk to your doctor before starting a new supplement, especially if you’re seriously ill or have a weakened immune system, it typically can’t hurt to give probiotics a try. I would recommend the natural probiotics found in yogurt, kombucha, or apple cider vinegar, but the capsule variety are also good.