Q: One summer, my go-to beverage was diet tonic water. I’d drink it all day (no alcohol). Toward the end of the summer, a routine blood test showed my liver values to be off the charts, although I felt fine.

While discussing this with my doctor, I remembered that years earlier, a similar erratic blood test had prompted another doc to ask what I had eaten or drunk the night before my blood was drawn. When I answered “Gin and tonic,” she said “That’s OK then.”

This time around, I quit tonic water for life. After a month, my liver values were going down. After three months, they were still elevated, though. My doc asked me whether I had any other peculiar eating habits.

I did. I had gotten in the habit of chomping cinnamon sticks all day. He did some research, and I quit cinnamon. After another month, my liver was normal. Conclusion: Apparently some people have a genetic predisposition to not be able to tolerate quinine. Cinnamon may also have an adverse effect on the liver for people like me.

A: Thanks for the reminder that even natural substances can have side effects. Quinine is known to cause dangerous blood disorders in some people. A study of adverse effects of this compound found that some sensitive individuals experienced liver toxicity after exposure to quinine-containing beverages, such as tonic water (American Journal of Hematology, May 2016).

Cinnamon is a bit more complicated. Several animal studies showed that it can help protect against liver damage due to acetaminophen toxicity. At high doses, however, cinnamon may harm the liver (Regulatory Toxicology and Pharmacology, June 2018).

Q: My retina specialist wants me to take PreserVision for macular degeneration. A daily dose has 80 milligrams of zinc. I also take a multivitamin containing 20 milligrams of zinc. Credible sources state that 40 milligrams/day is the safe upper limit for zinc intake. Should I be concerned?

A: You are correct that the tolerable upper limit established by the Food and Nutrition Board is 40 milligrams for adults. Daily doses above 50 milligrams can interfere with copper absorption. This can impair immune response and lower HDL cholesterol.

We suggest you check with your eye doctor about whether you might switch to a lower dose. The standard AREDS (Age- Related Eye Disease Studies) formulas contain 80 milligrams of zinc a day.

Q: I had to learn the hard way about drug interactions. I almost died from serotonin syndrome. My doctor took about 24 hours to pick up on it, and I’d never heard of it before.

I stay away from all selective serotonin reuptake inhibitor, or SSRI, antidepressants now. Drug interactions resulted in two seizures, including a grand mal seizure. My neurologist says trazodone and bupropion caused it. Now I have to stay on anticonvulsants for two years.

A: Combining the two antidepressants (bupropion and trazadone) could indeed increase the risk for serotonin syndrome. Symptoms may include anxiety, rapid pulse, tremors, muscle contractions, confusion, digestive upset and even seizures. Your story reminds us how crucial it is to avoid such dangerous combinations.

Busy physicians and pharmacists may not always double-check for potential interactions. That is why it is crucial for patients to be their own advocates when it comes to multiple prescriptions.

In their column, Joe and Teresa Graedon answer letters from readers. Send questions to them via www.peoplespharmacy.com.