Even though it is a natural product, turmeric may cause side effects. But, turmeric has not been extensively studied for medicinal use, so it is difficult to say what side effects might occur. Small studies do seem to suggest that most people tolerate turmeric well, experiencing little or no side effects. In these studies, turmeric side effects included nausea and diarrhea. When applied to the skin, turmeric can cause irritation and allergic reactions.