The vitamins contained in vitamin B complex are completely nontoxic even in high doses and usually, no side effects occur. Sensitivity to Vitamin B1 however, may sometimes be encountered if administration is at prolonged intervals, irregular, or if initial doses are low and suddenly increased. Liver dysfunctions could also predispose patients to hypersensitivity reactions. Nevertheless, it must be stressed that hypersensitivity to Vitamin B1 is very rare when given orally.