Oral drops: Adverse effects seldom occur following administration of Thiamine HCl (Vitamin B
1). Large doses of Riboflavin (Vitamin B
2) result in a bright yellow discoloration of urine. The astringent action of iron preparations sometimes produces gastrointestinal irritation and abdominal pain with nausea and vomiting when administered orally. These irritant side effects are usually related to the amount of elemental iron taken rather than the type of preparation. Oral liquid preparation containing iron salts may blacken the teeth and should be drunk through a straw. The feces of patients taking iron salts may be colored black.