Probiotics are live beneficial microorganisms, mostly bacteria and some yeasts that support digestive health when consumed in adequate amounts. These help to build healthy bacteria in your gut. It is better to get these from your food, aiming for at least two a day.  

To rebuild your gut it is helpful to take a probiotic for at least 8 to 12 weeks to see or feel results. For effectiveness, a good probiotic will have at least 10 billion CFU's, is to be taken daily on an empty stomach. Take these alongside at least two probiotic foods a day.

Specific strains work with specific conditions, eg taking an antibiotic, you would need a specific strain with a specific dose. In the event of candida you would take a different probiotic to what you take for when you are taking an antibiotic. Smart Strains is a recommended brand as they have a probiotic for each condition.