How much tonic water is too much?

In their column, Joe and Teresa Graedon answer letters from readers. Write to them in care of this newspaper or email them via their Web site: Their newest book is “Top Screwups Doctors Make and How to Avoid Them.”

Q: I am normally a mosquito magnet. By this time of year, I would usually have dozens of bites, and the itching would be intolerable. I would turn into a bloody mess from constant scratching.

This year, I have been drinking tonic water two or three times a day, and I haven’t had a mosquito bite in weeks. As an added bonus, I haven’t experienced leg cramps while cycling. In hot weather, I used to cramp up after two or three hours of hard riding.

Is there a limit on how much tonic you can drink before overdosing on quinine? I have read in your column that too much could be dangerous, but how much is too much?

A: Doctors used to prescribe quinine pills to prevent leg cramps. The standard dose was between 200 and 300 mg of quinine.

The Food and Drug Administration banned quinine for this purpose, but continues to allow it in tonic water. A liter normally has 83 mg of quinine. An eight-ounce glass would therefore have roughly 20 mg, about one-tenth the lowest dose doctors prescribed for leg cramps. Even three glasses daily should be OK as long as you are not sensitive to quinine.

Some susceptible people develop a dangerous blood disorder after even small doses of quinine. Symptoms of quinine toxicity include digestive upset, headache, ringing in the ears, visual disturbances, skin rash and arrhythmias.

Q: I am really upset about the latest information regarding the dangers of long-term use of PPI heartburn drugs. I have been taking one for several years for reflux.

I tried going off it and had terrible long-lasting heartburn the next day. I am going to try going off it again. Can I use something like Tums when I get that horrible heartburn, or do you have other suggestions?

A: Proton-pump inhibitors (PPIs) are popular for many digestive woes. They used to be perceived as super-safe, but over time disturbing complications have surfaced. These include kidney damage, dementia, fractures, pneumonia, diarrhea and certain nutritional deficiencies (iron, vitamin B-12 and magnesium).

As you discovered, stopping suddenly can lead to rebound heartburn that may last for weeks. To avoid this withdrawal, you might wean yourself gradually and add antacids, deglycyrrhizinated licorice, ginger and probiotics.

We are sending you our Guide to Digestive Disorders so you can learn more about the details. Anyone who would like a copy, please send $3 in check or money order with a long (No. 10), stamped (68 cents), self-addressed envelope to: Graedons’ People’s Pharmacy, No. G-3, P.O. Box 52027, Durham, NC 27717-2027. It also can be downloaded for $2 from our website:

Q: You’ve written that metformin helps keep cancer away. Then why doesn’t everyone take it? What are the side effects of metformin? Are the side effects serious enough to cancel the benefits of taking metformin if one is not diabetic?

A: Metformin is a pillar of Type 2 diabetes treatment. Recently, researchers have discovered an anti-cancer effect of metformin in the breast, pancreas, liver, colon, ovaries and prostate (Experimental and Clinical Endocrinology and Diabetes, May 2016).

Most doctors are cautious about prescribing metformin for cancer prevention because more research is needed.

Side effects can include digestive distress, rash, exhaustion and headache. The most serious, though rare, complication is lactic acidosis, associated with failure of the heart and other organs.