How does caffeine make you more alert and work as a cognitive enhancer if it reduces blood flow to the brain?


I’ve just read that a 250mg dose of caffeine can reduce blood flow to the brain by 22%-30%.

It seems counter intuitive to me that a chemical that restricts blood flow to the organ responsible for all mental operations actually improves our mental functioning.

There’s probably a simple answer but 22-30% seems like it would significantly impair the brain’s functioning

In: 129

250mg of caffeine is more than three shots of espresso. At that level of caffeine unless you’re a caffeine addict it will reduce your mental functioning.

But at lower dosages it can improve functioning in certain situations by turning off parts of your brain – it improves your ability to keep doing repetitive tasks by reducing your ability to feel tiredness, and making you less curious and distractible.

For the most part that’s how drugs that “improve” your mind tend to work – they temporarily break bits of your brain that you don’t want active given what you’re doing.

You don’t want self-consciousness when you’re socialising? Try some alcohol.

You don’t want to acknowledge your exhaustion when you’re working? Caffeine.

You don’t want to feel stressed by your stressful life? There are an array of options – although if we’re going with legal ones, this is Nicotine.

Of course, in all three of those cases the drug in question is addictive and will ultimately make your problems worse if you use it a lot. Caffeine overuse will mean you’re always tired and grumpy unless you have caffeine helping you ignore it. Alcohol will give you aches and pains, in addiction to crushing feelings of guilt for things you did while disinhibited that you can only quiet by drinking more alcohol.

Nicotine is the most addictive, and will make you CONSTANTLY stressed unless you’re actively smoking. It’s almost impossible to use in moderation, so don’t try. Alcohol and caffeine can be part of a healthy life, but nicotine just isn’t.

Caffeine inhibits receptors which give feelings of drowsiness, which makes you feel more focused and energized. Of course, this isn’t a replacement for sleep.


Anyway, blood flow and brain activity are correlated but the actual relationship is very complicated and difficult to study. The amount of blood flow to the brain being affected by caffeine also varies between people.

Side note: 250mg is a LOT. I consider myself a caffeine junkie and just thinking about taking in that much in one drink or over a short period of time makes me twitch. I’m happy topping out at 200mg at once, tyvm

It acts as a neurotransmitter, the fluid that carrier electrical signals between an axon of a neuron and a dendrite of another one.

There are two studies that have found this effect in an experiment with a relatively small samplesize of health young adults. While 17 and 45 is a small sample the measured magnitude seems consistent in both experiments. The first study from 1990 suggests that there is a minimum CBF of approximately 30ml/min/100g of tissue which acts as a tolerable minimum that avoids cognitive impairment and suggests that a regulatory mechanism preserves this minimum CBF even under the influence of caffeine. In the other hand caffeine acts antagonistic on adenosine receptors and can thereby delays physiological responses to fatigue and increase periods of alertness.