Consider this a little primer with conditions, probiotic names and prices.
Probiotics come in two main forms: food and dietary supplements. There are so many different brands and formulations and quality control is not well regulated. The effectiveness is specific to the disease and the dose taken.
1. Diarrhea after taking antibiotics (or to protect your GI tract when you take an antibiotic)-
DanActive - $5
Align - $50
Bio-K+ - $17-27
2. Ulcerative Colitis
Activa - $6
3. Irritable bowel
Any of the above. Activa yogurt is easy and effective. The active bacteria is Bifidobacterium animalis.
I always tell my patients to take probiotics along with antibiotics and after they are done to restore the normal gut bacteria that are wiped out by antibiotics. They are generally considered safe, even in children.