: 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
Energy Drinks Many energy drinks contain a lot of caffeine, which can leave you feeling jittery and anxious.
—
Jillian Kubala, Health, 8 Jan. 2026
Coffee contains caffeine, which can affect how your body absorbs and processes certain medications.
—Carrie Madormo, Verywell Health, 7 Jan. 2026
Now StriVectin is entering the arena with its form-fitting, hydrogel mask that uses a proprietary peptide blend and caffeine that depuff and tone the neck and jawline in 20 minutes.
—Jackie Fields, PEOPLE, 5 Jan. 2026
The apparent sweet spot aligns with guidance from health agencies like the U.S. Food and Drug Administration, which generally recommends limiting caffeine to about 400 milligrams a day, or roughly four cups of coffee.
—Deirdre Bardolf, FOXNews.com, 6 Dec. 2025
See All Example Sentences for caffeine
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Jillian Kubala, Health, 8 Jan. 2026
Coffee contains caffeine, which can affect how your body absorbs and processes certain medications.
—Carrie Madormo, Verywell Health, 7 Jan. 2026
Now StriVectin is entering the arena with its form-fitting, hydrogel mask that uses a proprietary peptide blend and caffeine that depuff and tone the neck and jawline in 20 minutes.
—Jackie Fields, PEOPLE, 5 Jan. 2026
The apparent sweet spot aligns with guidance from health agencies like the U.S. Food and Drug Administration, which generally recommends limiting caffeine to about 400 milligrams a day, or roughly four cups of coffee.
—Deirdre Bardolf, FOXNews.com, 6 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 15 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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