Drug Interaction Report

Cimetidine and Chloroquine: Interaction Details

A pharmacist-reviewed analysis of the Cimetidine and Chloroquine interaction: the documented clinical effects, severity rating, onset, mechanism, and management considerations, with cited references throughout.

AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature

Cimetidine

Tagamet
+

Chloroquine

Aralen®
Dr. Brian Staiger, PharmD, BCPS
Medically reviewed by
Dr. Brian Staiger, PharmD, BCPS
Updated Aug 8, 2026
Editorial policy · Data sources
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Interaction severity
Major
Potentially serious — often needs a change or close monitoring.
How we grade severity & evidence

Severity levels

  • Contraindicated: These should generally not be used together.
  • Major: Potentially serious — often needs a change or close monitoring.
  • Moderate: Can be significant — usually manageable with monitoring.
  • Minor: Usually limited clinical impact.

Evidence grades

  • Established: Well documented — supported by controlled studies or strong clinical data.
  • Probable: Good supporting evidence, though not definitively proven.
  • Suspected: Some evidence suggests this interaction, but it is not well established.
  • Possible: Limited or conflicting evidence; the interaction may occur.
  • Theoretical: Predicted from the drugs' pharmacology; not yet confirmed in people.

Ratings come from the documented interaction literature and are reviewed by a pharmacist. They describe the documented risk of the combination, not what will necessarily happen to you — your dose, timing, and health picture all matter.

Of 83 documented Cimetidine interactions, 48 are rated major — including this one.
Worried about symptoms right now? Contact your pharmacist or prescriber, or call Poison Control at 1-800-222-1222 (US). Call 911 for an emergency.
Onset
unspecified
Evidence
probable
Severity
Major

What happens

Chloroquine toxicity

Interaction Deep Dive

Cimetidine can inhibit the metabolism of chloroquine, increasing its plasma level. Avoid concomitant use of cimetidine and chloroquine21. In a controlled clinical study, the use of cimetidine with concurrent chloroquine resulted in an increased half-life (by greater than 50%) and a decreased clearance (about 50%) of chloroquine 3.

Why it happens (mechanism)

Cimetidine-mediated inhibition of chloroquine metabolism

Literature reports

1 report — tap to read

a) Concomitant administration of low-dose cimetidine (400 mg HS) and chloroquine sulfate (600 mg chloroquine base as a single dose) was reported to result in impairment of chloroquine elimination in healthy subjects 3. Combined therapy resulted in significant reductions in the oral clearance rate and prolongation of the half-life of chloroquine; a reduction in the AUC of monodesethylchloroquine (47%) was also observed. These data suggest that cimetidine inhibits the clearance of chloroquine secondary to inhibition of hepatic mixed-function oxidases. Multiple-dose studies are indicated to more fully evaluate this interaction.

Common questions

Can I take Cimetidine and Chloroquine together?

Chloroquine toxicity Always confirm with your pharmacist or prescriber before making any change.

How serious is the Cimetidine and Chloroquine interaction?

It is rated major. Potentially serious — often needs a change or close monitoring.

How quickly could this interaction happen?

The documented onset is "unspecified". The timing of this interaction is not well characterized.

How strong is the evidence for this interaction?

The evidence is graded "probable". Good supporting evidence, though not definitively proven.

Questions for your pharmacist

  • Does my dose of Cimetidine or Chloroquine need adjusting while I take them together?
  • What symptoms should prompt me to call you or my prescriber right away?
  • Does the timing of my doses matter for this combination?
  • Is there a safer alternative to one of these medications for me?

References (3)

  1. Product Information: Chloroquine phosphate oral tablets, chloroquine phosphate oral tablets. Rising Pharmaceuticals Inc (per DailyMed), Saddle Brook, NJ, 2018. DailyMed
  2. US Food & Drug Administration (FDA): Fact sheet for health care providers emergency use authorization (EUA) of chloroquine phosphate supplied from the strategic national stockpile for treatment of COVID-19 in certain hospitalized patients. US Food & Drug Administration (FDA). Silver Spring, MD. 2020.
  3. Ette EI, Brown-Awala A, & Essien EE: Chloroquine elimination in humans: effect of low-dose cimetidine. J Clin Pharmacol 1987; 27:813-816. PubMed
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Cimetidine

Keep reading about Cimetidine

All Cimetidine interactions (83)
Also serious with: Dofetilide Colchicine Octreotide Injection Meloxicam Injection
Chloroquine

Keep reading about Chloroquine

All Chloroquine interactions (332) Chloroquine drug information
Also serious with: Levomethadyl Pimozide Mesoridazine Levoketoconazole
Beyond drug–drug

These medications also interact with supplements

Prescription drugs aren't the whole picture — herbal and dietary supplements can interact with them too. From the evidence-graded Natural Medicines database:

Cimetidine + Activated Charcoal Pu-erh Tea St. John's Wort Adrafinil African Wild Potato Banderol Beer Bitter Melon + 87 more
Chloroquine + Activated Charcoal Hibiscus Sabdariffa Biofeedback Coffee Charcoal Dendrobium European Mandrake Fever Bark Ginkgo + 21 more

major · moderate · minor — check everything you take with our drug–supplement interaction checker.

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This information is for education, not a substitute for professional medical advice. Do not start, stop, or change any medication without talking to your pharmacist or prescriber.