brain fog

noun

: a usually temporary state of diminished mental capacity marked by inability to concentrate or to think or reason clearly

Examples of brain fog in a Sentence

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Examples are automatically compiled from online sources to show current usage. Read More Opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback.
Anxiety, panic attacks and depression were cited as the most impactful symptoms with women stating that brain fog and sleep disruptions affected them more than hot flashes. — Helen Carefoot, Flow Space, 7 Aug. 2026 According to The Sleep Clinic, common signs in women include chronic fatigue, insomnia, mood changes, morning headaches, brain fog and frequent nighttime urination. — Hanna Wickes, Miami Herald, 4 Aug. 2026 Common signs include fatigue, brain fog, low libido, weight gain, low mood and lack of motivation, according to the men and doctors who have shared their TRT experiences. — Samantha Agate, Kansas City Star, 30 July 2026 The disconnect matters because women in their 30s and early 40s may not realize that mood changes, sleep disruption and brain fog can be tied to hormonal shifts. — Hanna Wickes, Sacbee.com, 25 July 2026 See All Example Sentences for brain fog

Word History

First Known Use

1853, in the meaning defined above

Time Traveler
The first known use of brain fog was in 1853

Rhymes for brain fog

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Browse Nearby Words

brain-fever bird
brain fog
brain freeze
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Cite this Entry

“Brain fog.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/brain%20fog. Accessed 18 Aug. 2026.

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Medical Definition

brain fog

noun
: a usually temporary state of diminished mental capacity marked by inability to concentrate or to think or reason clearly
This brain fog can be a result of being overly stressed, tired, carrying extra weight, consuming too many calories or consistently consuming a diet poor in nutrients.—Kylie Helgens, The Gazette (Cedar Rapids, Iowa)
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