There are a few potential side effects to taking MCT oil, though they are relatively rare and tend to be mild. The most common side effects include upset stomach, diarrhea, and nausea. These symptoms typically resolve within a few days as your body adjusts to the oil. In rare cases, some people may experience more serious side effects like headaches, dizziness, or skin rashes. If you experience any of these symptoms, discontinue use of the oil and consult your doctor. Overall, MCT oil is safe for most people when used as directed.