Tamoxifen and Hydroxychloroquine: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Hydroxychloroquine
Tamoxifen
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.
What happens
Increased risk of retinal toxicity and increased risk of QT-interval prolongation
Interaction Deep Dive
Concomitant use of hydroxychloroquine with drugs known to induce retinal toxicity such as tamoxifen is not recommended3. Hydroxychloroquine has been associated with QT interval prolongation 4, ventricular premature contractions, and torsades de pointes 2. Coadministration with drugs that may induce cardiac arrhythmias is not recommended as life-threatening additive effects on the QT interval, including torsades de pointes, may occur. If concomitant use is required, consider close ECG monitoring at baseline and during therapy 1.
Why it happens (mechanism)
Additive retinal damage and QT interval effects
Literature reports
2 reports — tap to read
a) Hydroxychloroquine-associated QT interval prolongation was reported in a 41-year-old woman with congestive heart failure with systolic left ventricular dysfunction. Her comorbidities included hypertension, systemic lupus erythematosus, and stage 5 chronic kidney disease. One week after reinitiation of hydroxychloroquine therapy, a significant prolongation of the QT interval (QTc 614 msec) was observed during a routine ECG. Following treatment discontinuation of hydroxychloroquine, serial ECGs demonstrated a shortening of the QTc interval. The patient's QTc was 473 msec at a follow up 1 year after discharge 4.
b) QT prolongation and refractory ventricular arrhythmia were reported with chronic hydroxychloroquine use in a 67-year-old woman with systemic lupus erythematosus. The patient had been receiving prednisolone, theophylline, and hydroxychloroquine 200 mg/day for 1 year. The patient had a medical history of cirrhosis, hepatitis B virus related hepatoma with protal vein thrombosis, and asthma. The patient experienced a sudden episode of unconsciousness and generalized rigidity while at home. Although the patient regained consciousness within minutes and had no complaints of chest pain, palpitation, limb weakness, incontinence, or confusion, the episode recurred several times. Upon admission the ECG showed multiple ventricular premature contractions, torsade de pointes, and prolongation of the QT interval. Treatment with hydroxychloroquine was discontinued. Following medical management, ventricular arrhythmia subsided after 4 days and the QT interval shortened 2.
Common questions
Can I take Tamoxifen and Hydroxychloroquine together?
Increased risk of retinal toxicity and increased risk of QT-interval prolongation Always confirm with your pharmacist or prescriber before making any change.
How serious is the Tamoxifen and Hydroxychloroquine 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 "theoretical". Predicted from the drugs' pharmacology; not yet confirmed in people.
From our Q&A
Real reader questions about these medications, each personally answered by our pharmacist:
Questions for your pharmacist
- Does my dose of Tamoxifen or Hydroxychloroquine 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 (4)
- Product Information: PLAQUENIL(R) oral tablets, hydroxychloroquine sulfate oral tablets. Concordia Pharmaceuticals Inc (per DailyMed), Kansas City, MO, 2019. DailyMed
- Chen CY, Wang FL, & Lin CC: Chronic hydroxychloroquine use associated with QT prolongation and refractory ventricular arrhythmia. Clin Toxicol (Phila) 2006; 44(2):173-175. DOI
- US Food & Drug Administration (FDA): Fact sheet for health care providers emergency use authorization (EUA) of hydroxychloroquine sulfate supplied from the strategic national stockpile for treatment of COVID-19 in certain hospitalized patients. US Food & Drug Administration (FDA). Silver Spring, MD. 2020.
- Morgan ND, Patel SV, & Dvorkina O: Suspected hydroxychloroquine-associated QT-interval prolongation in a patient with systemic lupus erythematosus. J Clin Rheumatol 2013; 19(5):286-288. PubMed
Keep reading about Hydroxychloroquine
Keep reading about Tamoxifen
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:
major · moderate · minor — check everything you take with our drug–supplement interaction checker.
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