Feosol Original Side Effects

Generic Name: ferrous sulfate

Note: This page contains information about the side effects of ferrous sulfate. Some of the dosage forms included on this document may not apply to the brand name Feosol Original.

Not all side effects for Feosol Original may be reported. You should always consult a doctor or healthcare professional for medical advice. Side effects can be reported to the FDA here.

For the Consumer

Applies to ferrous sulfate: capsules, drops, elixir, liquid, tablets

Check with your doctor if any of these most COMMON side effects persist or become bothersome:

Constipation; darkened or green stools; diarrhea; loss of appetite; nausea; stomach cramps, pain, or upset; vomiting.

Seek medical attention right away if any of these SEVERE side effects occur while taking ferrous sulfate (the active ingredient contained in Feosol Original)

Severe allergic reactions (rash; hives; itching; difficulty breathing; tightness in the chest; swelling of the mouth, face, lips, or tongue); black, tarry stools; blood or streaks of blood in the stool; fever; severe or persistent nausea, stomach pain, or vomiting; vomit that looks like blood or coffee grounds.

For Healthcare Professionals

Applies to ferrous sulfate: compounding powder, oral capsule extended release, oral delayed release tablet, oral elixir, oral liquid, oral syrup, oral tablet, oral tablet extended release


Gastrointestinal side effects are generally dose-related and have included nausea, constipation, anorexia, heartburn, vomiting, and diarrhea. In addition, stools may appear darker in color in patients taking ferrous sulfate (the active ingredient contained in Feosol Original)

Oral preparations of ferrous sulfate may rarely cause Hemoccult-positive stools, patients with positive tests generally require further work-up.

Gastrointestinal side effects are dose-related with approximately 25% of patients experiencing side effects at a dosage of 325 mg three times a day.

Gastrointestinal discomfort may be minimized by initiating ferrous sulfate therapy at smaller doses and gradually titrating upwards until the desired dose is achieved.

Administering each dose with food may also minimize gastrointestinal discomfort. However, concurrent administration of ferrous sulfate with food may decrease the amount of iron absorbed.

Due to the small amount of iron released and absorbed, the use of enteric-coated or delayed release ferrous sulfate preparations may reduce gastrointestinal side effects; however, these products are not recommended for use.

Constipation may be relieved by administering docusate sodium 100 mg to 200 mg per day in addition to increasing the intake of oral fluids, such as water.


Other side effects have included stained teeth and iron overload (hemosiderosis). Secondary hemochromatosis due to prolonged iron ingestion has been reported rarely.

Stained teeth have primarily occurred following ingestion of ferrous sulfate liquid preparation. Liquid dosage forms should be diluted in juice or water and sipped through a straw to aid in prevention of staining.

Iron overload (i.e., hemosiderosis) has been reported in patients genetically predisposed, or have underlying disorders, that augment the absorption of iron. It has also occurred following administration of excessive parenteral iron therapy, combination of oral and parenteral iron, or in patients with hemoglobinopathies that were erroneously diagnosed as iron deficiency anemia. Hemosiderosis is treated with repeated phlebotomy or long-term administration of deferoxamine. The liver is particularly susceptible to toxicity in iron-overload states.


Immunologic side effects have rarely included gastroenteritis associated with Yersinia enterocolitica and Listeria monocytogenes in patients with iron overload status receiving treatment with deferoxamine.

It has been hypothesized that gastroenteritis is caused by bacteria that become virulent in the presence of iron overload resulting in a systemic infection. Treatment consists of discontinuing deferoxamine and initiating appropriate antimicrobial therapy.


Local side effects have included gangrene.

Localized corrosion has been reported in a pregnant woman taking ferrous sulfate (tablet) that lodged in a Meckels diverticulum.

There have also been reports of wax-matrix ferrous sulfate tablets (delayed-release) lodging in the bowels of patients with strictures.


Metabolic side effects have included decreased absorption of thyroxine (T4).

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