Functional neuroimaging of cognition impaired by a classical antihistamine, d-chlorpheniramine

Nobuyuki Okamura, Kazuhiko Yanai, Makoto Higuchi, Jun Sakai, Ren Iwata, Tatsuo Ido, Hidetada Sasaki, Takehiko Watanabe, Masatoshi Itoh

Research output: Contribution to journalArticlepeer-review

103 Citations (Scopus)


1. Antihistamine induced cognitive decline was evaluated using positron emission tomography (PET) measurement of histamine H1 receptor (H1R) occupancy and regional cerebral blood flow (rCBF). 2. Cognitive performance in attention-demanding task deteriorated dose-dependently and the effects were statistically significant after the treatment of 2 mg of d-chlorpheniramine. There was no significant change in subjective sleepiness in the same dose. 3. The regional blockade of H1R was observed mainly in the frontal, temporal and anterior cingulate cortices, and the intravenous administration of d-chlorpheniramine as a therapeutic dose (2 mg) blocked over 60 of H1R in the frontal cortices. 4. The results from activation study using visual discrimination tasks demonstrated that enhanced activity in the right prefrontal and anterior cingulate cortices as well as a decreased activity in the left temporal and frontal cortices and midbrain after the treatment of d-chlorpheniramine. 5. There were no changes in global CBF for the subjects treated with 2 mg d-chlorpheniramine (pre; 44.8 ± 3.3 ml dl-1 min-1 vs post; 44.4 ± 4.7 ml dl-1 min-1). 6. The results indicated that the attention system of human brain could be altered by therapeutic doses of H1R antagonists. These findings provide the information as to the potential risk of antihistamines in our daily activities.

Original languageEnglish
Pages (from-to)115-123
Number of pages9
JournalBritish Journal of Pharmacology
Issue number1
Publication statusPublished - 2000


  • Antihistamines
  • Brain
  • Cerebral blood flow
  • Chlorpheniramine
  • Cognition
  • H1 receptor antagonists
  • Positron emission tomography
  • Receptor occupancy
  • Sedation in man

ASJC Scopus subject areas

  • Pharmacology


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