Most probiotics are inactivated in the stomach because stomach acid has a pH between 1.8 and 3.5, which is a strong acidic environment, so most of the acid-intolerant probiotics will be inactivated by stomach acid.
Bifidobacterium and Lactobacillus are commonly used clinically to regulate intestinal flora and relieve intestinal discomfort. Most probiotics will be inactivated by stomach acid, but not all probiotics will be inactivated, and those that survive will enter the intestines to play a role.
Nowadays, many probiotics used as medications are made in the form of enteric-coated tablets, which will dissolve and exert their activity only when they reach the intestines. In addition, stomach acid is diluted and the pH rises after a meal, so it is recommended that probiotics be taken 2 hours after a meal.
If you need to use probiotics to regulate intestinal flora, please do so under the guidance of your doctor.