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I like coffee, but caffeine seems to 'wire' me much more extremely than most other people. I feel energized or even shaky after less than half a normal cup, and a whole 8 ounces will usually cause me to sweat or make my heart race uncomfortably.

Even decaffeinated coffee seems to have this effect, which seems strange to me (although I am aware that it still contains a small amount of caffeine). I typically drink green tea instead of coffee, since the effect is more mild.

Is this an indication that my body metabolizes caffeine faster (or slower?) than normal? What else can cause caffeine sensitivity?

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    There's a possible chance it could be a placebo due to expectations from watching e.g. television which depicts coffee as making you jittery.
    – Rapptz
    Mar 31, 2015 at 23:19
  • @Rapptz True. Although this has been the case for 2+ years of small to moderate caffeine consumption.
    – Nate Barbettini
    Mar 31, 2015 at 23:21
  • Nothing definitive enough for an answer, but I know of other individuals reporting a high sensitivity to caffeine. My guess is that people metabolize it differently. I have never had coffee, but I've had caffeinated soft drinks from time to time. I almost never drink them--so it can't be chalked up to tolerance--but I have never noticed any effect from drinking them. As for the idea that you're experiencing a placebo effect, I'm guessing you could eliminate that possibility by actually measuring your heart rate after having a friend give you something with and without caffeine. Science! :)
    – msouth
    Apr 1, 2015 at 0:36
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    @msouth To really rule out the placebo effect, though, it'd have to be a double-blind test with a coffee-like control. Or a caffeine tablet, maybe? :)
    – Nate Barbettini
    Apr 1, 2015 at 5:00
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    @msouth Is the experiment sentient in this case? Wouldn't that mean that it could affect its own outcome?
    – Nate Barbettini
    Apr 15, 2015 at 14:03

2 Answers 2

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Caffeine metabolism has to do with your genetic makeup. The slower you metabolize caffeine, the more effect it will have on you. The cause for the differences that people have in how fast they metabolize caffeine has to depend on the CYP1A2 gene. Variants of this gene can cause you to metabolize faster or slower. The C allele variant in the AHR gene, which controls the turning on and off the the CYP1A2 gene, is common in people who have a high metabolism for caffeine. You probably do not have this variant. That with a few other factors that depend on variants in your DNA are the reason that caffeine has a strong effect on you.

Caffeine Consumption

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  • Spot on. According to 23andMe, I have one of the "fast" alleles and one of the "slow", so my overall caffeine metabolism is slow.
    – Nate Barbettini
    Apr 15, 2015 at 14:10
  • There are also some drugs that inhibit the CYP1A2 enzyme. See this Pharmacy Times article for some of those drugs.
    – Katherine Lockwood
    Dec 7, 2016 at 2:21
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All caffeinated beverages like coffee (even decaffeinated) and soft drinks give short bursts of energy, temporarily raise blood pressure, and reduces blood flow to inactive limbs.

Soon after you drink coffee (containing caffeine), it’s absorbed through the small intestine and dissolved into the bloodstream and it’s able to penetrate the blood-brain barrier and enter the brain.

Your sensitivity really depends on your body tolerance threshold (e.g. renal threshold for blood) and your average daily intake, in other words it's determined by the efficiency of the human body to process and metabolize caffeine. It's usually to do with person’s unique DNA which determines to what degree a given amount of caffeine will affect a person (as described in the other answer).

See also: What are the side effects of drinking too much coffee?

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    Would it be possible to add sources for this?
    – anongoodnurse
    Apr 18, 2015 at 6:24
  • Hi kenorb, even though you have cited multiple sources in your other post, it's important to cite the relevant ones here too, or else we'd be chasing citation tails. Please include them as @anongoodnurse already asked.
    – Dave Liu
    Feb 12, 2016 at 21:38

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