Levothyroxine and Chloroquine: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Chloroquine
Levothyroxine
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
An increase in the thyroxine stimulating hormone level and decreased levothyroxine effectiveness
Interaction Deep Dive
Concomitant administration of levothyroxine and chloroquine may decrease the effect of levothyroxine and increase serum TSH levels1. If chloroquine is administered to patients already receiving thyroid replacement therapy, monitor TSH levels.
Why it happens (mechanism)
Induction by chloroquine of levothyroxine metabolism
Literature reports
1 report — tap to read
a) When a 52-year-old white female taking thyroxine sodium (125 mcg daily) for hypothyroidism received chloroquine (100 mg daily) and proguanil (200 mg daily) for two months as prophylaxis against malaria, her thyroid stimulating hormone (TSH) concentration increased to 44.8 mU/L (normal range 0.35-6.0 mU/L). Her TSH levels returned to normal within one week after discontinuing chloroquine and proguanil. The same prophylaxis was prescribed 16 months later for an intended travel to Indonesia. Her TSH levels prior to her departure, when she came back, and eight weeks after starting the prophylaxis were 3.2, 26, and 54.7 mU/L, respectively. When she came back, free triiodothyronine, free thyroxine, and thyroglobulin concentrations were 2.7 pmol/L (normal range 2.6-5.9), 11 pmol/L (normal range 6-18), and 1.1 pg/L (normal range less than 25), respectively. Four weeks after the end of the second prophylactic course, her TSH and free triiodothyronine concentrations had returned to normal. It is suggested that the mechanism of this interaction is the induction by chloroquine of liver enzymes involved in the catabolism of thyroid hormone 1.
Common questions
Can I take Levothyroxine and Chloroquine together?
An increase in the thyroxine stimulating hormone level and decreased levothyroxine effectiveness Always confirm with your pharmacist or prescriber before making any change.
How serious is the Levothyroxine and Chloroquine interaction?
It is rated minor. Usually limited clinical impact.
How quickly could this interaction happen?
The documented onset is "delayed". Effects tend to build up gradually over days to weeks.
How strong is the evidence for this interaction?
The evidence is graded "probable". Good supporting evidence, though not definitively proven.
From our Q&A
Real reader questions about these medications, each personally answered by our pharmacist:
Questions for your pharmacist
- Does my dose of Levothyroxine 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 anything you'd monitor while I'm on both?
References (1)
- Munera Y, Hugues FC, Le Jeunne C, et al: Interaction of thyroxine sodium with antimalarial drugs. Br Med J 1997; 314:1593.
Keep reading about Chloroquine
Keep reading about Levothyroxine
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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