Caffeine: Pharmacokinetics & Pharmacodynamics

Instructor: Danielle Haak

Danielle has a PhD in Natural Resource Sciences and a MSc in Biological Sciences

Humans consume caffeine daily, but do you know how it affects the body and why? This lesson will examine how caffeine moves in the body and how it has a stimulant effect on the body. Grab a cup of coffee and keep reading!

Caffeine Breakdown

Caffeine is a naturally-occurring substance found in many plant species, and humans can consume it for its stimulant effects - this is why coffee perks you up in the morning (or afternoon or whenever you need it). Though it is naturally occurring, the Food and Drug Administration (FDA) still tracks its use in products and has labeled caffeine as both a food substance and as a drug.

For the purposes of this lesson, we'll be investigating how caffeine moves throughout the body once it's consumed (pharmacokinetics), as well as how and why it affects the body like it does (pharmacodynamics). Though each person responds to drugs like caffeine differently, there are some generalizations we can apply across the board.

The molecular structure of caffeine
Caffeine structure

Pharmacokinetics of Caffeine

When you consume caffeine through eating or drinking something caffeinated, what happens? Well, imagine you drink a cup of coffee. Initially, that coffee goes to your stomach to start the digestion process. Your digestion system absorbs the caffeine, and it enters the blood stream. The time it takes for caffeine to be absorbed depends on a person's health, if they've eaten recently, and their general reaction to caffeine (some people are more susceptible to its effects than others).

Once in the blood stream, caffeine circulates and eventually reaches the liver, where the liver processes it into smaller components, and these smaller components are called metabolites. There are three metabolites we should know about:

  • 84% of caffeine is broken down into paraxanthine, which affects the levels of fat in the blood and helps keep a person alert.
  • 12% of caffeine is broken down into theobromine, which causes the blood vessels to widen and promotes urine production (one reason you need to use the bathroom so much when you're drinking a lot of coffee or caffeinated soda).
  • 4% of caffeine is broken down into theophylline, which causes the airways to widen, making it easier to breathe.

Finally, caffeine is able to cross the blood-brain barrier, which just means it can move from the blood stream into the brain, which is how it works as a stimulant. Specifically, once in the brain, caffeine blocks the effects of a neurotransmitter called adenosine, a molecule that promotes sleep. It also temporarily increases the production of dopamine, a chemical substance in the brain that is associated with increased concentration.

Pharmacodynamics of Caffeine

Now that you know where caffeine and its metabolites go in the body, the effects caffeine has on the body make more sense. The central nervous system (the brain and spinal cord) are most impacted by caffeine consumption, and the effects usually last a few hours in healthy adults. To review, these effects include:

  • Increased alertness and feeling awake, predominantly because of how caffeine blocks adenosine in the brain and because it increases blood flow through widened blood vessels
  • A boost in memory and concentration, mainly because it increases the production of dopamine
  • Pain reduction, especially headaches, because widened blood vessels promote blood flow

There is also some evidence suggesting that regular caffeine consumption helps prevent certain brain disorders, though more research is underway to further investigate this claim.

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