Vitamins are generally believed to be safe to use, more so the B- complex group of vitamins. However, while this is true of smaller doses of vitamins, with large doses, also called therapeutic doses, there can be many unpleasant side effects or even serious morbidity.
There are mild adverse effects due to niacinamide which are generally self limiting, and usually subside once use of niacinamide is stopped. The common side effects of vitamin B-3 are nausea, vomiting and headache. Other adverse effects include dizziness, skin flushes and itching. A note of caution here is that, as with any medicine, if the adverse effects do not disappear or subside on stopping the oral use of niacinamde, the patient must consult a doctor immediately.
There are also major side effects or reactions to vitamin B-3 use. These include dark colored urine and bloody or black stool. Other adverse effects include swelling of the feet and hands (a condition called edema), abdominal pain or aches, and loss of consciousness. Neurological reactions (involving the nervous system) include tingling and numbness of hands or legs and vision disturbances. The patient may also suffer from loss of appetite and yellow discoloration of the eyes and skin (a condition called jaundice), which results from damage to the liver, a known side effect of vitamin B3. Bleeding from the stomach may result in coffee colored vomiting. The major side effects of niacin occur usually when large doses (greater than 3 gms. /day) are taken.
A small number of patients may develop minor and in some cases even serious allergic reactions to vitamin B3. These reactions include chest discomfort and inability to breathe, a condition called dyspnea. Other allergic reactions include swelling of the lips and face and edema of the voice box, skin rashes and urticaria.
There are certain conditions where patients must exercise caution while using niacinamide. These include pregnancy, diabetes, heart disease, gall bladder pathology, allergies, gout, liver conditions, kidney diseases, and stomach conditions. Niacinamide can be used in pregnancy in small doses (less than 30 mg/ day). However, larger doses must be avoided to the extent possible due to possible detrimental effects on the fetus. The recommended dose of niacin for pregnant or breast-feeding women is 30 mg per day for women under 18 years of age, and 35 mg for women over the age of 18 yrs. Diabetic patients must use caution as niacinamide is known to cause an increase in blood sugar. Thus patients suffering from diabetes must monitor their blood sugar carefully before and during the use of niacinamide. Liver conditions and kidney diseases are grey areas for the use of niacinamide, as this vitamin is known to exacerbate these conditions. Such patients can receive adequate doses of niacinamide, but only under the supervision of a doctor. Very high doses of niacinamide can also precipitate an attack of gout in patients prone to high blood uric acid levels. Heart patients also need to be careful while using high or therapeutic doses of niacinamide due to the danger of irregular heart beats.
For more information see Vitamin Niacinamide.