Good ol’ quinine:
Quinine Sulfate Oral Side Effects
See also Overdose section.
Headache, flushing, unusual sweating, nausea, ringing in the ears, decreased hearing, dizziness, blurred vision, and temporary changes in color vision may occur. Less common side effects may include signs of low blood sugar (e.g., sweating, shakiness, confusion, extreme hunger). If you experience these symptoms, promptly drink some fruit juice or have a snack, and call your doctor immediately. 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 may experience these side effects, but with frequent visits to your doctor, this risk can be reduced.
Tell your doctor immediately if any of these rare but very serious side effects occur: signs of a serious immune system problem (e.g., unusual tiredness, joint/muscle aches, unusual fever, butterfly-shaped facial rash, swollen glands), easy bruising/bleeding, signs of serious infection (e.g., high fever, severe chills, persistent sore throat), signs of a sudden loss of red blood cells called hemolytic anemia (e.g., severe tiredness, brown urine, pale lips/nails/skin, rapid breathing at rest), signs of severe liver problems (e.g., persistent nausea/vomiting, abdominal pain, severe weakness, yellow skin/eyes, unusually dark urine), decrease in the amount of urine.
Seek immediate medical attention if any of these rare but very serious side effects occur: chest pain, severe dizziness, fainting, fast/irregular heartbeat.
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.
Call your doctor for medical advice about side effects. In the US, you may report side effects to the Food and Drug Administration (FDA) at 1-800-FDA-1088.
In Canada, you may report side effects to Health Canada at 1-866-234-2345.
Back in the day when it was on the shelf in front of the counter, it was rumored among teen-age women to induce miscarriage, as well.
But folks should by all means run it by their docs first :)