: a bitter alkaloid C8H10N4O2 found especially in coffee, tea, cacao, and kola nuts and used medicinally as a stimulant and diuretic
Examples of caffeine in a Sentence
Her doctor told her to avoid caffeine.
Recent Examples on the Web
Cap caffeine in the early afternoon.
—
Sarah Klein, Outside, 1 Jan. 2026
To lessen the risk of digestive issues from drinking, doctors also recommend eating before drinking, limiting intake to two drinks a day, staying hydrated and not mixing alcohol with caffeine, which can further stimulate the gut.
—Deirdre Bardolf, FOXNews.com, 31 Dec. 2025
Just limit your consumption to about two to three cups a day, and try to cut off caffeine by noon to protect your sleep.
—Jenna Anderson, Health, 31 Dec. 2025
The over-consumption of caffeine makes some people jittery, so these results might seem confusing.
—Sheah Rarback, Miami Herald, 31 Dec. 2025
See All Example Sentences for caffeine
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Sarah Klein, Outside, 1 Jan. 2026
To lessen the risk of digestive issues from drinking, doctors also recommend eating before drinking, limiting intake to two drinks a day, staying hydrated and not mixing alcohol with caffeine, which can further stimulate the gut.
—Deirdre Bardolf, FOXNews.com, 31 Dec. 2025
Just limit your consumption to about two to three cups a day, and try to cut off caffeine by noon to protect your sleep.
—Jenna Anderson, Health, 31 Dec. 2025
The over-consumption of caffeine makes some people jittery, so these results might seem confusing.
—Sheah Rarback, Miami Herald, 31 Dec. 2025
See All Example Sentences for caffeine
Cite this Entry
“Caffeine.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/caffeine. Accessed 2 Jan. 2026.
Copy CitationKids Definition
caffeine
noun
caf·feine
ka-ˈfēn 
ˈka-ˌfēn
: a bitter stimulating compound found especially in coffee, tea, cacao, and kola nuts
Medical Definition
caffeine
noun
caf·feine
ka-ˈfēn, ˈka-ˌ; ˈkaf-ē-ən
: a bitter alkaloid C8H10N4O2 found especially in coffee, tea, and kola nuts and used medicinally as a stimulant and diuretic
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