NutriStack
Cimetidine and Green Tea Extract, a caution.
Cimetidine inhibits CYP1A2, the main enzyme that clears caffeine. Caffeine-containing green tea extract taken with cimetidine can produce higher and longer-lasting plasma caffeine levels, raising the risk of jitteriness, insomnia, palpitations, and elevated blood pressure. A controlled study showed cimetidine reduced caffeine clearance significantly.
One pair, every claim cited. The two substances, the type, the mechanism, the recommendation, and the primary literature.
Same shape as the other 1,729 pairs in the public database.
From the interaction database
What the row says.
Every entry follows the same shape: what is happening, the mechanism, the recommendation, and the primary literature.
At a glance
- Substances
- Cimetidine and Green Tea Extract
- Pair type
- Caution
- Evidence (highest tier)
- Moderate
- Source citations
- 2 sources
- Stack Score effect
- −5 to your Stack Score (per scored caution row).
- Scope
- Supplement × Prescription
- Last verified
- May 30, 2026
Caution · Moderate evidence
Caution
What is happening. Cimetidine inhibits CYP1A2, the main enzyme that clears caffeine. Caffeine-containing green tea extract taken with cimetidine can produce higher and longer-lasting plasma caffeine levels, raising the risk of jitteriness, insomnia, palpitations, and elevated blood pressure. A controlled study showed cimetidine reduced caffeine clearance significantly.
Mechanism. Caffeine is metabolized by hepatic CYP1A2. Cimetidine inhibits CYP1A2 more strongly than any other H2 blocker, prolonging caffeine half-life and raising peak plasma concentrations.
Recommendation. If you take cimetidine, prefer a decaffeinated green tea extract or limit total caffeine intake. Watch for signs of caffeine excess like racing heart or insomnia, especially in the first week of combining them.
Sources (2)
- Broughton LJ, Rogers HJ. Decreased systemic clearance of caffeine due to cimetidine. Br J Clin Pharmacol. 1981;12(2):155-9. PMID 7306430
- Martínez C, Albet C, Agúndez JA, et al. Comparative in vitro and in vivo inhibition of cytochrome P450 CYP1A2, CYP2D6, and CYP3A by H2-receptor antagonists. Clin Pharmacol Ther. 1999;65(4):369-76. PMID 10223772
Stack Score
How this pair moves the number.
Effect on the composite score
If both Cimetidine and Green Tea Extract are in the same stack, this pair applies −5 to your Stack Score (per scored caution row).
The full algorithm, the clamping rules, and four worked stacks are documented at /methodology/stack-score.
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