: 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
Swapping your morning coffee for lemongrass tea reduces caffeine exposure, which may benefit some people with hypertension (high blood pressure).
—
Md Published, Verywell Health, 6 June 2026
Fans can customize the Refresher with either lemonade or coconut milk, as well as choose the level of caffeine and B vitamins in it.
—Chiara Kim, PEOPLE, 5 June 2026
Energy drinks are often loaded with caffeine and sugar, along with other stimulants that can put extra strain on the cardiovascular system.
—Dr. Sanjay Bhojraj, CNBC, 4 June 2026
In another case, a federal lawsuit filed in April 2026 in Texas also targeted an energy drink company over allegations that inadequate warning labels contributed to a teenager’s October 2025 death, raising broader questions about marketing and caffeine safety in products aimed at younger consumers.
—Anthony Thompson, USA Today, 3 June 2026
See All Example Sentences for caffeine
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Md Published, Verywell Health, 6 June 2026
Fans can customize the Refresher with either lemonade or coconut milk, as well as choose the level of caffeine and B vitamins in it.
—Chiara Kim, PEOPLE, 5 June 2026
Energy drinks are often loaded with caffeine and sugar, along with other stimulants that can put extra strain on the cardiovascular system.
—Dr. Sanjay Bhojraj, CNBC, 4 June 2026
In another case, a federal lawsuit filed in April 2026 in Texas also targeted an energy drink company over allegations that inadequate warning labels contributed to a teenager’s October 2025 death, raising broader questions about marketing and caffeine safety in products aimed at younger consumers.
—Anthony Thompson, USA Today, 3 June 2026
See All Example Sentences for caffeine
Cite this Entry
“Caffeine.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/caffeine. Accessed 10 Jun. 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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