Sympathomimetic effects of paraxanthine and caffeine in humans

Neal L. Benowitz*, Peyton Jacob, Haim Mayan, Charles Denaro

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

139 Scopus citations


Caffeine is metabolized extensively (on average 80%) to paraxanthine. With regular caffeine consumption, average serum levels of paraxanthine are two thirds those of caffeine. Both caffeine and paraxanthine competitively and nonselectively inhibit adenosine receptors in vitro. To examine the contribution of paraxanthine to the pharmacologic activity of caffeine, we administered to 12 subjects in a crossover design oral caffeine (2 or 4 mg/kg) versus placebo or oral paraxanthine (same dose as caffeine) versus placebo, each after 3 days of methylxanthine abstinence. Both caffeine and paraxanthine significantly increased diastolic blood pressure, plasma epinephrine levels, and free fatty acids. Caffeine and paraxanthine produced a similar magnitude of response at 4 mg/kg; however, caffeine appeared to produce greater responses than paraxanthine at 2 mg/kg. Caffeine and paraxanthine have similar sympathomimetic actions. The activity of paraxanthine needs to be considered in understanding the clinical pharmacology of-caffeine, particularly with chronic, repetitive caffeine consumption.

Original languageEnglish
Pages (from-to)684-691
Number of pages8
JournalClinical Pharmacology and Therapeutics
Issue number6
StatePublished - 1995
Externally publishedYes


FundersFunder number
National Institute on Drug AbuseP50DA001696


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