Why does caffeine not work for some people?

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It is three in the afternoon, and you are in need of a quick energy boost before you leave work in a few hours time. So you head down to the nearest café (if your pantry is not blessed with the best espresso machine already) to get yourself a cup of coffee. Upon a sip of that robust liquid made from the finest Arabica beans, you instantaneously feel alert and ready to seize the world.

Well, not for everyone, at least.

As we all know, the reason why a cup of coffee is able to keep most people alert is due to a particular compound found in the drink called “caffeine”. Caffeine can not only be found in coffee, but in other consumables such as tea, cocoa, carbonated beverages and energy drinks as well.

How does caffeine work?

At every waking moment, neurons in your brain fire away and while this goes on, the neurons release a chemical called “adenosine”. What adenosine does is that it binds to adenosine receptors that are in the brain, slowing down nerve cells, and causing drowsiness to a person, making them feel sleepy.


Whenever a person consumes something which contains caffeine, the caffeine would bind to the adenosine receptors. This is because, to a nerve cell, caffeine looks like adenosine. Once all the receptors have been bound with caffeine, the nerve cells would fail to recognise the existence of adenosine. Therefore, instead of causing drowsiness, caffeine does the opposite; it speeds nerve cells up.


Now that the caffeine has taken up all the space meant for adenosine, the rate at which the neurons fire in the brain will begin to increase. The pituity gland, which produces important hormones, sees this increase as a form of emergency. As a result, it would release hormones to inform the adrenal glands to produce adrenaline. Adrenaline, as we know, is the “fight or flight” hormone which causes several things to occur to your body.

But why doesn’t it work for me?

Different people react differently to caffeine and there are two possible reasons why:

1. You just may lack the genes for it

Researchers from the Harvard School of Public Health, as well as Brigham and Women’s Hospital, have found that genetics play a major role as to why the effect of caffeine varies from person to person.

The liver metabolizes caffeine through an enzyme called CYP1A2. Since every person has a unique genetic make-up, the amount of this enzyme produced by a person affects their overall caffeine sensitivity; someone who produces low levels of this enzyme eliminates the caffeine slower, while those with high levels would be able to get rid of caffeine much quicker. The latter, those with high levels of CYP1A2, explains one of the reasons why it seems as though caffeine does not work for them.


2. Your tolerance is high

As with a lot of things (e.g. alcohol, certain medication), your body will eventually develop a tolerance to how these substances affect your body. Similarly, for those who consume large amounts of caffeine, they may eventually not feel its effect fully if they go on taking in the same amount, every day.

To support this, I have gathered a number of anecdotal evidences from a couple of baristas who work in different cafés. The reason why I picked these people, was simply due to the fact that they would have to consume copious amounts of coffee everyday, in order to aid them in calibrating their espresso machines and brewing the perfect cup of coffee.

Out of the three that I asked, all of them except one was “immune” to the effects of caffeine. For the one who still felt the effects, it could potentially mean that he is highly sensitive to caffeine, seeing that it causes him to hyperventilate after consuming a certain amount.

Being a former barista with 4 years of experience, I have developed a tolerance for caffeine; drinking coffee is akin to drinking regular water.

The ways to feel the effects of caffeine

Based on the two reasons provided earlier, the only way for you to feel the effects of caffeine is through increasing the amounts of that you consume.

For those who are tolerant, you might want to consider taking a break from consuming any caffeine at all, to “reset” your tolerance.


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