Estrogen Therapy Inhibits Caffeine Metabolism (J Clin Pharmacol, 1999)

Tier 1: Established: peer-reviewed research or government health authority
Publisher: Journal of Clinical Pharmacology, via PubMed · Published: August 11, 2026 · Accessed: August 11, 2026

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Claims this source supports

• Estrogen replacement therapy significantly inhibits caffeine metabolism (cytochrome P450 1A2-mediated) in postmenopausal women, slowing caffeine clearance.
• Because estrogen changes how fast caffeine is cleared, the same cup of coffee can linger longer in the body at different hormone levels.
• The effect is measurable at clinical doses: 12 healthy postmenopausal women showed reduced caffeine clearance during estrogen therapy.