Vitamin D3 Oral, or Cholecalciferol Oral, is a dietary supplement. Most of the people consume diet which does not provide them adequate quantity of Vitamin D3. This induces Vitamin D3 deficiency. Vitamin D3 Oral helps body absorb calcium. It is an over-the-counter and prescription medicine which is used to fight Vitamin D3 deficiency. The side effects of Vitamin D3 Oral are rare. Double dose or unintentionally high dose can boost Vitamin D level. In such case the side effects include - Nausea and vomiting - Stomach cramps - Contipation - Increased urination - Increased thirst - Loss of appetite - Fatigue - Mood swings Vitamin D3 interacts with medicines containing calcium, phosphate, magnesium, calcitriol and Vitamin D.