These surprising foods can be toxic in excess

By Ryan Black
Published July 26, 2021

Key Takeaways

When people hear the term “overdose,” they might think of drug abuse or accidental prescription misuse. But there are plenty of foods that can cause an overdose, too—including some unexpected dietary staples.

Most people won’t ingest enough of any one food to approach a serious toxicity level or potentially fatal overdose, but confirmed overdoses have indeed happened. 

Here are five unexpected food items that can cause serious health problems or overdose.


Tea is often lauded for its health benefits. It boasts antioxidant qualities and immune-boosting power, and is even potentially protective against heart disease. 

But tea, particularly black tea, also contains a lot of oxalate, a compound that can accumulate in the kidneys, leading to kidney stones and, in extreme cases, kidney failure. 

One patient discovered this the hard way, and made headlines in the process. A letter to the New England Journal of Medicine detailed a patient who presented with acute oxalate nephropathy as a result of his gallon-a-day ingestion of black iced tea. The patient had no personal or familial history of renal disease, and doctors determined his best course of care was dialysis. 

While an extreme quantity of iced tea daily can be dangerous, smaller amounts may prove hazardous for nephrology patients, who may want to stick to no more than a few glasses.


Potatoes seem innocent enough—but their roots and leaves are poisonous, and sometimes the spuds themselves can be, too. That’s because of an abundance of solanine and chaconine, two natural toxins known as glycoalkaloids, which are present in the green and sprouted parts of a potato. Chlorophyll is responsible for the green color, and it’s nontoxic itself, however, it indicates the presence of solanine and chaconine inside the potato. 

According to Poison Control, “The entire potato plant contains glycoalkaloids, but the highest concentration is found in the leaves, flowers, ‘eyes,’ green skin, and sprouts. The lowest concentration is found in the white body of the potato. Toxicity is increased by physical injury to the plant, immaturity (green potato), low storage temperature, and storage in bright light.”

Poisoning from these toxins can cause vomiting, abdominal pain, diarrhea, confusion and, rarely, even death. Cooking potatoes will not remove the toxins, and there are even past cases of mass potato-poisoning incidents after green potatoes were accidentally served to schoolchildren—notably in 1979 and 1983.

Bottom line? Buy only as many spuds as you need, store them in a cool, dry place, and peel them before you ingest them. If the potatoes are green or have grown sprouts, it’s time to throw them away.  

Black licorice

Black licorice is perhaps the most polarizing snack on this list, and it’s the only one that comes with a Halloween-themed overdose warning video from the FDA

Black licorice contains a compound called glycyrrhizin, derived from licorice root, that can cause the consumer’s potassium levels to drop. Low potassium can lead to serious complications, from weakness and fatigue to heart arrhythmias.

Despite its playful theme, the FDA’s warning video was likely aimed at adults over 40—or with a history of heart problems—rather than children. 

According to the FDA, one would need to consume 2 ounces or more of licorice candy daily for about 2 weeks straight to risk hypokalemia. But excessive licorice consumption could still cause complications for those who already suffer from conditions that cause potassium deficiency. 

Licorice root is also sold as a supplement and is often used as an alternative treatment for many digestive issues. Those with potassium concerns who wish to use it should look for "deglycyrrhizinated" licorice root. 


While most know that chocolate can be fatal if ingested by the family dog, few may realize it can be poisonous to humans, too—but only if you eat a much larger quantity.

Chocolate contains the alkaloid theobromine, a mild natural stimulant whose effects cause jitters, like fellow alkaloids nicotine and caffeine. While that chemical might produce the soothing feeling some people get from a piece of rich, dark chocolate, it’s still a stimulant—and too much of any stimulant will never be a good thing.

The reason why theobromine isn’t nearly as harmful for humans as it is for their pets is that we can metabolize it much better. The LD50—what would be the lethal dose for 50% of the population—for theobromine in humans is 1,000 mg/kg of body weight. Comparatively, theobromine LD50 for dogs is 300 mg/kg and only 200 mg/kg for cats. 

So, how much chocolate would produce a fatal theobromine overdose in a 165 lb human? Popular Science estimated that, in one sitting, you would need to eat more than 700 milk chocolate bars, or more than 300 dark chocolate bars. Not impossible, but it seems other factors—like a serious sugar rush—would become a concern far before the theobromine.


The specter of a coffee overdose might be less surprising to anyone who has had a few too many cups of the bean beverage before breakfast. The fast and noticeable physiological effects of coffee are what make it appealing for so many people.

But too much caffeine can overwhelm the heart and central nervous system, leading to heightened anxiety and heart palpitations. The average cup of coffee has about 70 to 150 mg of caffeine. Consumption of up to 400 mg per day of caffeine is considered safe for healthy adults, according to research, but experts caution not to exceed that limit too frequently.

About 10 grams is considered a potentially fatal overdose for a human—that would be well over 100 cups of coffee in a sitting. But there are other potent ways of ingesting caffeine, like energy drinks and caffeine pills, and caffeine overdose deaths do occur from time to time.   

Even a mild caffeine overdose, however, can produce uncomfortable jitteriness, anxiety, and arrythmia—so best to not let the Starbucks habit get out of hand.

Everything in moderation

Thankfully, it would be difficult for most people to ingest a fatal dose of any of these foods. But overconsumption can still cause avoidable health complications. If you find yourself binging on one food item in particular, or have underlying health conditions that could be exacerbated by any of the items above, it may be wise to reassess.

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