But just to back up: Probiotics are live beneficial microorganisms1 that live in and on the human body, mostly in the digestive tract. They offer a wide range of health benefits that support a healthier immune system, digestive system function, and detoxification. Probiotic supplements are becoming increasingly popular as more people include them in their daily routine. After a few weeks of taking the right probiotic, you should start noticing the beneficial effects. Here’s how you can tell it’s doing its job.