Quinine is a bitter compound that comes from the bark of the cinchona tree. The tree is most commonly found in South America, Central America, the islands of the Caribbean, and parts of the western coast of Africa. Quinine was originally developed as a medicine to fight malaria. It was crucial in reducing the death rate of workers building the Panama Canal in the early 20^th century.

Quinine, when found in small doses in tonic water, is safe to consume. The first tonic waters contained powdered quinine, sugar, and soda water. Tonic water has since become a common mixer with liquor, the most well-known combination being gin and tonic.

The U.S. Food and Drug Administration (FDA) allows tonic water to contain no more than 83 parts per million of quinine, because there can be side effects from quinine.

Today, people sometimes drink tonic water to treat nighttime leg cramps associated with circulatory or nervous system problems. However, this treatment is not recommended. Quinine is still given in in small doses to treat malaria in tropical regions.

Quinine’s primary benefit is for the treatment of malaria. It’s not used to prevent malaria, but rather to kill the organism responsible for the disease. When used to treat malaria, quinine is given in a pill form.

Quinine is still in tonic water, which is consumed around the world as a popular mixer with spirits, such as gin and vodka. It’s a bitter beverage, though some manufacturers have tried to soften the taste a little with added sugars and other flavors.

Quinine in tonic water is diluted enough that serious side effects are unlikely. If you do have a reaction, it may include:

• nausea
• stomach cramps
• diarrhea
• vomiting
• ringing in the ears
• confusion
• nervousness

However, these are more common side effects for quinine taken as a medication. Among the most serious potential side effects associated with quinine are:

• bleeding problems
• kidney damage
• abnormal heartbeat
• severe allergic reaction

Keep in mind that these reactions are primarily linked to quinine, the medication. You would have to drink about two liters of tonic water a day to consume a day’s dose of quinine in pill form.

If you’ve had a bad reaction to tonic water or quinine in the past, you should not try it again. You may also be advised against taking quinine or drinking tonic water if you:

• have an abnormal heart rhythm, especially a prolonged QT interval
• have low blood sugar (because quinine can cause your blood sugar to drop)
• are pregnant
• have kidney or liver disease
• are taking medications, such as blood thinners, antidepressants, antibiotics, antacids, and statins (these medications may not preclude you from taking quinine or drinking tonic water, but you should tell your doctor about these and any other medications you take if you’re prescribed quinine)

While a gin and tonic and vodka and tonic are staples at any bar, tonic water is becoming a more versatile beverage. It’s now mixed with tequila, brandy, and just about any other alcoholic beverage. Citrus flavors are often added, so if you see the term “bitter lemon” or “bitter lime,” you know the drink includes tonic water with a sour fruit flavor added.

However, tonic water isn’t just used to mix with spirits. Chefs may include tonic water in batter when frying seafood or in desserts that also include gin and other liquors.

If tonic water is your mixer of choice, you’re probably safe to have a little now and then. But don’t drink it thinking it will cure nighttime leg cramps or conditions such as restless leg syndrome. The science isn’t there for tonic water or quinine to treat these conditions. See a doctor instead and explore other options. But if you’re traveling to a part of the world where malaria is still a threat, ask about the use of quinine to treat the disease if you’re unfortunate enough to contract it.