STEM Critical Thinking: Can Caffeine kill you?

Can Caffeine Kill you?

Which would you prefer to drink- a cup of caffeine or a cup of trichloroethylene? When most people are asked this question, they would respond with caffeine- and they would be dead wrong.  Well, maybe they just do not have enough information, at least this was the hypothesis put forth by AP Environmental Science students. They thought that the students picked caffeine because it was what they were familiar with.  If they knew more about trichloroethylene, would that change their response?   They added to their survey and went back out and asked again to see if the context and information was the problem.  This time the question was given some background:

Caffeine occurs naturally in coffee, tea, and chocolate and is added to sodas and other types of drinks and foods. Trichloroethylene is a solvent used to remove grease and also a common ingredient in glue and paint removers.  If given a choice and you had to pick one, would you rather drink a cup of caffeine or a cup of trichloroethylene?

What do you think the respondents said? 

Of course, they still said caffeine and again they would have made the fatal choice.  So why is this?  After a long discussion about the activity, students came to this conclusion,

“People rely more on their previous knowledge and do not ask good questions when faced with an unfamiliar choice.”

A good question that the respondents should have asked, do you mean a cup of coffee with caffeine or a cup of caffeine?

One of the problems with this activity is that people made assumptions.  They assumed that the students meant a cup of coffee with caffeine and not a cup of just “caffeine”.  Also people do not know how much caffeine is in a cup of coffee or how that would relate to the consumption of an entire cup. The amount of caffeine in a normal human diet is not enough to cause illness, but just 50 times that amount would be fatal.

Here is a short video explaining:

So does this mean that you should make sure your will is in order before you brew that next cup of coffee?  Probably not.  Everyone does react differently to coffee but the normal person would need to consume a very large amount for it to be toxic.

In the defense of the respondents to the survey, no one should really be consuming trichloroethylene either.  While it is not as toxic as caffeine in similar amounts, it can cause serious health problems if consumed in a large enough dose. ( for more information about TCE, go to and use code ATR01)

What is a dose and why does that matter? 

To measure a chemical’s short-term toxicity, scientists carry out something called a “dose/response” study.  The word dose refers to the total amount of substance to which an individual is exposed to through the mouth, lungs or skin. 

In short, all chemicals and substances can be toxic and lethal, it just depends on the dose. Even water can kill you if you drink too much too quickly.  Tragically in Georgia, this happened to a Douglas County Football player in 2014. 

Back in the 1500’s a Swiss doctor named Philippus Aureolus Theophrastus Bombastus von Hohenheim- Paracelsus, wrote

“All substances are poisons, there is none which is not a poison.  The right dose differentiates a poison from a remedy” 

This is why it is so important to take medicine in the correct dose.  Even something that feels harmless, like a vitamin, can be toxic if you take too many of them.  For example, England found that just by reducing the package size for Tylenol, they could reduce the number of people that overdosed.  This is also why you cannot buy a BIG bottle of children’s Tylenol or Motrin. The size is restricted. 

The intention is that if a child was to get the top off of the bottle and drink the entire contents, they still would not get a dose large enough to be fatal.  Granted, they may have liver or kidney damage and suffer other ill effects but the hope is that it would not kill them. Since it is so easy to get Acetaminophen and people do not read the directions, it is commonly on the Top Fatal Drugs list each year alongside Heroin, Cocaine, and Methamphetamine.

So how do drug companies know what dosage to put on those bottles?

They use a number called the L50 .  The L50 is the number at which 50% of the tested organisms died.  For example, if a drug is tested on mice, the L50 is the amount that killed 50% of more of the mice in that particular experiment.  The lower the L50, the more dangerous or toxic the compound.  This number is also just an estimate and that alone can be dangerous.  It is also important to know that different species have different toxic compounds.  For example, a person can eat a substantial amount of chocolate and not get sick; whereas, the same amount given to a dog could be fatal. Below is a table of the L50 of some common compounds.

Dosage is also crucial for parents to understand. Not all 2-year-olds weigh the same amount as each other or respond the same to medicines.  That is why parents should not really rely on these dosages on the bottle to dispense medicine. The American Academy of Pediatrics recommends that parents get the specific dose for the typical Over the Counter Medicines from their pediatrician and write these dosages on the bottle or inside their medicine cabinet.  The child’s doctor calculates this based on the child’s weight.  You can also do this from home using information provided by companies, like Tylenol.  Most of the major brands have a dosage chart based on weight on their website, it is just too complicated to place onto the bottle so they do a smaller version with averages for the product display.

Want to know the levels of toxicity for humans, check out the table below which compares some common compounds and ranks them in order of toxicity.

What do you think Paracelsus meant when he wrote that the right dose differentiates a poison from a remedy?  Can you think of a substance that is good for you at one dose and poisonous at another?  Why might it be useful to know the LD 50 of a chemical?  How might you use this information?  If a compound is shown to be practically nontoxic, can you conclude that the compound will have no adverse effects on humans or living things?  What other tests and information might be useful to make this decision? We look forward to continuing the discussion in the comments below or feel free to tweet at us (@Georgia_STEM) or look us up on facebook ( or even send an Email.

Thanks for reading and we hope you have STEMtastic day!





4 thoughts on “STEM Critical Thinking: Can Caffeine kill you?

  1. Think of all the things that could kill us but we’re all just too comfortable with the surrounding of it to ever truly know the danger.

  2. It’s a very interesting change in the casual mindset.
    The thought of something that most people have never even heard of before can actually be less
    harmful than something most people especially Americans in so many of our daily drinks. This fact about any+substance being able to kill really makes you think. Still gonna drink my coffee though.

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