Can I experience side effects from taking nutritional supplements? In general, when taken as prescribed, nutritional supplements do not have any side effects. However, when you begin to take nutritional supplements for the first time, you may experience some detox symptoms during the first few weeks. These symptoms are due to the fact that some supplements are cleansing your body from accumulated toxins (detox), and in most cases, are not a sign of intolerance or allergy to the ingredients. These symptoms may include skin impurities, nausea and fatigue, but are just temporary until the body has cleansed itself of the toxins. Some people, however, do have allergies to certain ingredients such as shellfish, which is why you should seek advice from a medical professional experienced in nutritional medicine.