The Different Side Effects of Caffeine

Last Reviewed 07/03/2014

The Different Side Effects of Caffeine

If you rely on coffee to provide a pick me up on the job, you're definitely not alone, especially if you work in the health care profession. Doctors and nurses rely on coffee to make it through their workday, according to a recent survey commissioned by Career Builder and Dunkin’ Donuts. The survey showed that members of those two medical professions were the ones who relied on coffee the most; others in the top 10 include hotel workers, teachers, and machinery operators.

I can testify to the medical profession’s reliance on coffee from my days as a resident and intern in the 1970s, a time we doctors none-too-fondly refer to as “the days of the iron men.” We used to be on call every other night, often surviving on one or two hours of sleep during a 36-hour shift.

Despite our sleep deprivation, we had to perform. It was imperative that we kept our minds sharp to deal with emergencies, an overwhelming multitude of complex patients, and our studies, so how did we do it? You guessed it. We drank a steady stream of coffee in the hospital, the library, and our dorms. We drank it at all hours of the day and night to keep us razor sharp—or at least awake—pushing way beyond our usual physical limits.

At the time, it seemed like the only solution to the long hours demanded of doctors-in-training. There are benefits to caffeine consumption, certainly, but there are also unwanted side effects of caffeine as well.

Side effects of caffeine can be obvious for some people: jitteriness and the infamous “caffeine crash” once the juice clears its way out of your system. But for others, the side effects of caffeine are not so obvious.

Caffeine’s Side Effects: A Case Study

One of my patients was a fellow I’ll call Ed, who sought help for his cardiac arrhythmia, high blood pressure, and insomnia. He also struggled with a thought disorder, for which a psychiatrist was treating him with potent psychoactive drugs. These medications were important, because they allowed him to function day-to-day.

Ed was aware that his heartbeat was rapid—as high as 150, even when he was resting. During Ed’s many office visits his blood pressure was also as high as 180–190/110–130.

My first inclination after studying Ed’s history was to blame his fast heartbeat on his psychoactive drugs. However, when Ed told me that he was drinking from 10 to 20 cups of coffee a day, I realized that Ed had a side effect of caffeine known as “caffeinism”—an overdose state.

Caffeinism is a definite clinical syndrome, characterized by specific caffeine side effects: central nervous system (CNS) effects like agitation, irritability, and inability to sleep, as well as peripheral signs that include high heart rate, high blood pressure, and cardiac arrhythmias.

And the medical literature indicates that caffeinism as a side effect of caffeine has been reported in people consuming as little as 500 to 1,000 mg per day—right around the average consumption for most people.

And don’t be misled by research saying that caffeine doesn’t cause the arrhythmia known as atrial fibrillation (AF). I’ve seen too many patients over the years who drank multiple cups of coffee or caffeinated sodas, and ate chocolate, then suddenly came down with AF. I’ve seen AF triggered by just a bit of chocolate after dinner.

There are caffeine-sensitive people for whom even a little bit of chocolate can trigger AF. If you consume any caffeine, and feel palpations, you must suspect that it’s a side effect of caffeine. Test it and if you can make the connection, stop the caffeine or cut down your intake.

Caffeine Side Effects and Other Medical Conditions

Anxiety disorders and panic attacks affect up to one-third of the patients who seek out cardiologists. Most panic attacks result in cardiovascular sensations that include chest pain, extreme shortness of breath, rapid heartbeat, and even a fear of dying. In one study, even moderate doses—four to five cups of coffee per day—precipitated panic attacks as a side effect of caffeine in about half of the subjects.

During pregnancy, caffeine also poses a risk to the unborn child. Because a human fetus retains caffeine longer than an adult, caffeine should be used cautiously by any woman who is trying or likely to conceive. Some research indicates that as little as 150 mg of caffeine per day in the first trimester of pregnancy can cause intrauterine growth retardation, and 300 mg doses nearly doubled the risk of spontaneous abortion.

Dealing With Caffeine Side Effects

The most common caffeine source is coffee. The average five-ounce cup of coffee contains 100 mg of caffeine, and 80 percent of adults consume between 3 and 5 cups of coffee every day (that’s 300 to 500 mg of caffeine). This probably underestimates caffeine consumption when you realize that many of us consider a large 20-ounce mug-full to be a “cup” of coffee.

Most people describe enhanced alertness, mental acuity, and competency after caffeine ingestion. The brain is usually the first organ to reap benefits, experiencing a greater sense of wakefulness and less fatigue. Caffeine is quick, and most of us notice its “kick” within only 20 minutes. Caffeine reaches significant blood levels in only 30 to 45 minutes and peaks in about two hours.

Caffeine has some medicinal benefits, too.

  • In the 1850s, caffeine was the treatment of choice for asthma in Europe. Caffeine can enhance the relaxation of small airways, or bronchioles, in the lungs. This relaxation makes it easier to breathe.
  • Caffeine can relieve migraine headaches, by constricting cerebral blood vessels. Migraines are caused by excessive blood pooling and subsequent tissue irritation in the brain.
  • Caffeine can also decrease appetite and increase urine flow, as well as induce contractions of the gall bladder, preventing it from becoming sluggish.

What’s My Take on Caffeine?

I advise that you use caffeine with extreme caution and in moderate doses. A “pick-me-up” of one cup of coffee or two cups of tea in the morning will not cause any undue caffeine side effects. But remember that caffeine is a drug. Be honest with yourself about your tolerance of and dependence on caffeine. Many of us are hooked on it. And there’s even a side effect of caffeine if your caffeine is significantly reduced: a withdrawal syndrome.

Many people report headache, drowsiness, and fatigue when withdrawing from caffeine. They also report impaired intellectual and motor performance, difficulty with concentration, and other psychological complaints. Though these symptoms disappear over time, they can sometimes linger for as long as two weeks.

I recommend that you limit your ingestion of caffeine to the equivalent of one or two cups of coffee per day to keep caffeine side effects at bay. At doses of less than 200 mg daily, you’ll be less likely to develop a dependence on caffeine while still benefiting from some of its favorable psychoactive and psychological effects. And if you’re someone with cardiac arrhythmia, hypertension, or anxiety and panic disorders, or if you’re trying to conceive, you’re better off switching to caffeine-free products. 


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