I keep reading on one forum or another about a few people having reactions when they take probiotics and wondering if they are allergic. I have an answer for that! I doubt it is an allergy, as allergies are swift, 25 mins to an hour, and usually cause such harsh reactions, they tend to be life threatening.. However, a person can be intolerant, or hyper-senitive to probiotics. It is not all that uncommon.. My son suffered all his life with IBS and nothing I did helped.. One day a psychologist told me that many people with autism have issues with yeast, which I can find no proof or studies for, however, it was a new idea and I tried her suggestion of probiotics and anti-fungal with a candidiasis specific diet. VOILA! A normal BM after about 5 to 7 days..Thought I'd found my answer... then after he was on the probiotics for about a month, he got diarrhea! Psychologist said he just had too many and to back him off some. For the next year, it was probiotics when he needed a BM and then I was doctoring diarrhea longer and longer..He lost more than 40 pounds.. along with his appetite. And the diarrhea was more uncomfortable to him then the constipation. Well I had changed so many things at once, I had no idea what was doing what, but didn't take me long to figure it out. He was reacting to the probiotics. He got more and more sensitive to them too, as I kept giving them in smaller and smaller doses and even switched types and brand.. Now he is even very sensitive to and reacts to higrade yogurt (the kind with real live cultures in it). And the diarrhea he gets with the probiotics sensitivity smells very bad, just as if he has been on a round of antibiotics for too long or is ill. Awful acrid smell. So the very thing that heped him the most, now tears him up. And before the diarrhea starts, his stomach is in turmoil... Sometimes he loses his appetite, sometimes he eats me out of house and home as his stomach gnaws and he thinks he is hungry.. He drinks a lot too.. Probably trying to sooth the gnawing or burning. He is autistic and his communication is very limited, so I have to watch, observe, test and try.. But he is definitely intolerant/senitive to probiotics, and I know this for sure as I started watching for other signs as well, and every time he has just one 12 billion CFU, it starts to come on him by next day... The gnawing gut, hyper-appetite or none at all.. Sleeps a lot.. and by third day, a rosey rash right at the back of his neck that he scratches bloody... The rash also reaches around the top of the stomach just under his rib cage.. Sometime the cheek of his butt gets rosey too. Only happens when given the probiotic and believe me I have given him many trials, since everyone kept assuring me that he can't be sensitive to probiotics. I personally, can take the strongest "P" on the market and even triple up on the dose, and I never notice I'm taking a thing!! But the smallest amount now, will pop out on him in full force within 3 days! I don't want him to become allergic to them, so we are backing off for a long while.. Sometimes a sensitivity to an item will totally disappear when removed for awhile. SO that's the game plan. I just wanted to let some of you inquisitive folks out there know that 'yes indeed', probiotics can run you in circles if you have a sensitive system to them, and many people do! Also, you can get tested for sensitivities right on line, just by sending in a few of your hairs.. The test is very inclusive and only cost about $80. If you don't see something on the test you want tested, just ask... They throw in 5 or 6 extra items for free. It is a reputable lab and test. Just Google "testyourintolerance".