When I first took creatine from an Amazon dealer I had gut problems. I later bought a "micronized" creatine (similar to https://bulevip.com/es/3418-optimum-nutrition-creatina-powde...) and did not experience any gut problems. Taking the same product now for 3 years. Inbetween I used some other variant from time to time and have the theory that some vendors sell a not clean product that interferes with your gut.