Health knowledge and news provided by doctors.

Are Some Coffee Drinkers at Risk of a Caffeine Overdose?

Timothy Boyer Ph.D.'s picture
Too much caffeine can cause heart arrhythmias.

A recent news story reveals yet another death diagnosed as caused by caffeine toxicity. While medical professions consider that drinking enough cups of coffee to reach toxic levels is nearly impossible to achieve, it is not totally without ill effects. Here’s what you need to know about how many cups is right for you.


Coroners determined the cause of death this past month of a 38-year-old man as being due to caffeine toxicity. In fact, blood levels tests showed that he had a blood concentration of 282mg of caffeine per milliliter of blood—“the equivalent of about three-and-a-half 250ml cans of Red Bull or seven cans of Coke” states the news story.

Recent numbers report that the lethal dose (LD-50) of caffeine in humans is estimated to be about 150 to 200 milligrams per kilogram of body mass, which comes to about 80 to 100 cups of coffee taken within a short period.

Caffeine Content in Beverages

Just to give you an idea of how the caffeine content differs among common caffeinated drinks, here is a quick list rating the caffeine content from lowest to highest:

• Cola drink (335ml): 40mg

• Black tea (250ml): 63mg

• Instant coffee (250ml): 79mg

• Filter coffee (250ml): 90mg

• An espresso drink (250ml) with 2 shots: 120-160mg

• Energy drink (250ml): ranges up to 300mg

While it is fairly clear that under normal circumstances, drinking 80-100 cups is pretty much a nearly-impossible amount of coffee to drink in one day, there are reports of as little as 2 grams of caffeine (roughly 20 cups of coffee) resulting in overdoses that required hospitalization.

The reason for this is that some people have a genetic predisposition for caffeine sensitivity that can seriously limit just how much coffee they can safely consume. However, this is referring to toxicity. Even under much lower concentrations of caffeine from coffee, a person can still become nauseous; experience a fluttering sensation in the chest indicating a possible arrhythmia; suffer from muscle twitching, and even experience psychosis.

For example, I have been drinking coffee of all types for many years on a daily basis, probably equivalent to about 6 shots of espresso total which comes to about 360 milligrams per day. Not an overly large amount of caffeine, and my body tolerates it fairly well. Much to many friends’ surprise, it does not really matter when I drink coffee, I have no problem falling asleep…ever. I’m like a dog in that sense. Find a comfortable spot and I’m out.

However, you take someone else who has not “trained” their body for years to handle this amount of caffeine, and you wind up with someone who is so wired you might believe that they are demon-possessed…and then no one gets any sleep.

According to the Mayo Clinic, my caffeine levels are at an acceptable number. On their website they state that: “Up to 400 milligrams (mg) of caffeine a day appears to be safe for most healthy adults. That's roughly the amount of caffeine in four cups of brewed coffee.”

Follow eMaxHealth on YouTube, Twitter and Facebook.
Please, click to subscribe to our Youtube Channel to be notified about upcoming health and food tips.

However, if you drink more than 4 cups of coffee a day, you may want to cut back or switch to decaf if you are experiencing side effects such as:

• Headache
• Insomnia
• Nervousness
• Irritability
• Frequent urination or inability to control urination
• Fast heartbeat
• Muscle tremors

There is Such a Thing as Caffeine Addiction

But what about addiction?

I do not believe that I am a caffeine addict; however, some opinions differ. Many health professionals state that a dependency on caffeine is actually medically-categorized as a mental illness and has been added to the Psychiatric Association's Mental Health Bible, the "Diagnostic and Statistical Manual of Mental Disorders." Health experts explain that whether it’s alcoholism, or cocaine, or heroin abuse, caffeine is a drug and when you have symptoms of withdrawal of any type, it meets the criteria in their classification system.

One indication of a dependency problem is when you go cold turkey on coffee and you experience 3 out of the 5 following symptoms:

• Headache
• Fatigue or drowsiness
• Depressed mood
• Irritability
• Flu-like symptoms (muscle aches or nausea)

Sounds like a typical Monday for me.

But seriously, too much coffee at the very least can be the root of digestion problems, ulcers, insomnia, and anxiety. As such, regardless of what the latest news says about what is the average amount of coffee people drink and what levels they consider to be healthful or harmful, moderation and common sense should be your guide. Listen to your body and it will tell you whether you had enough coffee for the day and should switch to something else…like beer for example.

If you are pregnant and wondering if you should change your caffeine habits during your pregnancy, here is an informative article about a link between caffeine and estrogen and race.

Estrogen Changes Linked to Caffeine Consumption Show Racial Differences

Timothy Boyer has a Ph.D. in Molecular and Cellular Biology from the University of Arizona. For 20+ years he has been employed as a freelance health and science writer. Timothy continues writing about science with a focus on the connection between coffee and healthy living. For continual updates about the benefits of coffee on your health, you can also follow Timothy on Twitter at TimBoyerWrites.

Images courtesy of Pixabay


Review of Caffeine-Related Fatalities along with Postmortem Blood Concentrations in 51 Poisoning Deaths” Journal of analytical toxicology 41(3):1-6 · February 2017.

Caffeine: How much is too much?” The Mayo Clinic