SIDE EFFECTS: Blurred vision, nausea, vomiting, abdominal cramps, headache, and diarrhea may occur. If any of these effects persist or worsen, tell your doctor or pharmacist promptly.

Remember that your doctor has prescribed this medication because he or she has judged that the benefit to you is greater than the risk of side effects. Many people using this medication do not have serious side effects.

Tell your doctor immediately if any of these unlikely but serious side effects occur: bleaching of hair color, hair loss, mental/mood changes (such as confusion, personality changes, unusual thoughts/behavior, depression), ringing in the ears, darkening of skin/tissue inside the mouth, worsening of skin conditions (such as dermatitis, psoriasis), sun sensitivity.

Some side effects only occur rarely with daily, long-term use (over weeks to years). Seek immediate medical attention if any of these very serious side effects occur: signs of a poorly pumping heart (such as tiredness, shortness of breath, swelling legs/ankles), muscle weakness, severe vision changes (such as light flashes/streaks, difficulty reading, complete blindness), hearing loss.

Tell your doctor immediately if any of these rare but very serious side effects occur: signs of serious infection (such as high fever, severe chills, persistent sore throat), signs of decreased red blood cells (such as tiredness, pale lips/nails/skin, fast heartbeat/breathing with normal activity level), signs of liver disease (such as severe stomach/abdominal pain, extreme tiredness, yellowing eyes/skin, dark urine), easy bruising/bleeding.

Seek immediate medical attention if any of these rare but very serious side effects occur: severe dizziness, fainting, fast/slow/irregular heartbeat, seizures.

A very serious allergic reaction to this drug is rare. However, seek immediate medical attention if you notice any symptoms of a serious allergic reaction, including: rash, itching/swelling (especially of the face/tongue/throat), severe dizziness, trouble breathing.

This is not a complete list of possible side effects. If you notice other effects not listed above, contact your doctor or pharmacist.

In the US -

Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

In Canada - Call your doctor for medical advice about side effects. You may report side effects to Health Canada at 1-866-234-2345.

Read the Aralen (chloroquine) Side Effects Center for a complete guide to possible side effects »

PRECAUTIONS: Before taking chloroquine, tell your doctor or pharmacist if you are allergic to it; or to hydroxychloroquine; or if you have any other allergies. This product may contain inactive ingredients, which can cause allergic reactions or other problems. Talk to your pharmacist for more details.

Before using this medication, tell your doctor or pharmacist your medical history, especially of: a certain enzyme problem (glucose-6-phosphate dehydrogenase deficiency-G6PD), vision/eye problems, hearing problems, kidney disease, liver disease, regular alcohol use/abuse, psoriasis, a certain blood disorder (porphyria), seizures.

This drug may cause blurred vision or rarely make you dizzy. Do not drive, use machinery, or do any activity that requires alertness or clear vision until you are sure you can perform such activities safely. Avoid alcoholic beverages.

Before having surgery, tell your doctor or dentist about all the products you use (including prescription drugs, nonprescription drugs, and herbal products).

This medication may make you more sensitive to the sun. Avoid prolonged sun exposure, tanning booths, and sunlamps. Use a sunscreen and wear protective clothing when outdoors.

Chloroquine may cause a condition that affects the heart rhythm (QT prolongation). QT prolongation can infrequently result in serious (rarely fatal) fast/irregular heartbeat and other symptoms (such as severe dizziness, fainting) that require immediate medical attention. The risk of QT prolongation may be increased if you have certain medical conditions or are taking other drugs that may affect the heart rhythm (see also Drug Interactions section). Before using chloroquine, tell your doctor or pharmacist if you have any of the following conditions: certain heart problems (heart failure, slow heartbeat, QT prolongation in the EKG), family history of certain heart problems (QT prolongation in the EKG, sudden cardiac death).

Low levels of potassium or magnesium in the blood may also increase your risk of QT prolongation. This risk may increase if you use certain drugs (such as diuretics/"water pills") or if you have conditions such as severe sweating, diarrhea, or vomiting. Talk to your doctor about using chloroquine safely.

During pregnancy, this medication should be used only when clearly needed. It may harm an unborn baby. While you are pregnant, traveling to an area with malaria places you and your infant at much higher risk of death and other problems. Discuss the risks and benefits of malaria prevention with your doctor.

This drug passes into breast milk and the effect on a nursing infant is unknown. Discuss the risks and benefits with your doctor before breast-feeding.