Ohiras are my favorites. Kind of pricey though; even from iHerb. I like them, because of the cultures they use; and the duration of the culturing.
It is possible that your friend may be taking something like medication that is destroying the flora. Hopefully it is not some IBS problem. Recommend that he continues yogurt, even though he is taking the supplement. The soured milk is good. Most fermented, nonalcoholic, things are good for the intestines.
Once upon a time, when I was 8 y/o, my mom had to take me to the doctor with some sever pain in my lower intestine. The doctor laughed and said it was constipation. He said, "Drink more water." The idiot. My mom was mad, because she was a weave mill worker and did not make very much money; as well as supporting 3 children by herself. I've had constipation problems ever since that time. These last few years, now in my 60s, help has been probiotic supplements, digestive bitters, and occasional herbs.