Many labels for probiotics are lacking important information.
Georgetown researchers analyzed 93 different bottles of probiotics from four large national retailers.
Only 35-percent were likely to be medically effective based on clinical evidence.
Experts say the remaining might have also been supported by clinical studies.
But they were not able to track any of it down due to insufficient labeling.
The probiotics that had fewer strains and were cheaper tended to be the ones that the scientists could track down the clinical evidence.
The scientists looked at the label for the strain of bacteria and yeast, the strain that was said to be present at a beneficial dose, and at least one controlled *human* study supporting its use.