Before taking quinine, tell your doctor or pharmacist if you are allergic to it; or to quinidine or mefloquine; 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: previous serious side effects with quinine (such as blood problems), family/personal history of a certain enzyme problem (glucose-6-phosphate dehydrogenase deficiency-G6PD), a certain eye nerve problem (optic neuritis), hearing problems (such as ringing in the ears), a certain nerve/muscle disease (myasthenia gravis), heart rhythm problems (such as atrial fibrillation/flutter), kidney problems, liver problems.

This drug may make you dizzy or blur your vision. Alcohol or marijuana (cannabis) can make you more dizzy. Do not drive, use machinery, or do anything that needs alertness or clear vision until you can do it safely. Limit alcoholic beverages. Talk to your doctor if you are using marijuana (cannabis).

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

Quinine may cause a condition that affects the heart rhythm (QT prolongation). QT prolongation can rarely cause serious (rarely fatal) fast/irregular heartbeat and other symptoms (such as severe dizziness, fainting) that need medical attention right away.

The risk of QT prolongation may be increased if you have certain medical conditions or are taking other drugs that may cause QT prolongation. Before using quinine, tell your doctor or pharmacist of all the drugs you take and 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 quinine safely.

Older adults may be more sensitive to the side effects of this drug, especially QT prolongation (see above).

During pregnancy, this medication should be used only when clearly needed. Discuss the risks, benefits, and treatment options with your doctor. Untreated malaria is a serious condition that can harm both a pregnant woman and her unborn baby.

This drug passes into breast milk. However, this drug is unlikely to harm some nursing infants. Your doctor will test your infant for a certain enzyme deficiency (glucose-6-phosphate dehydrogenase deficiency-G6PD) before you breastfeed. Consult your doctor before breastfeeding.