Istradefylline and Haloperidol: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Haloperidol
No brand names on recordIstradefylline
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 haloperidol exposure and an increased risk of haloperidol-related adverse events, including QTc interval prolongation
Interaction Deep Dive
Coadministration of haloperidol (CYP3A substrate) and CYP3A4 inhibitors may increase haloperidol exposure, which may increase haloperidol-related adverse events, including QTc interval prolongation. Increased QTc has been observed when haloperidol was given concomitantly with ketoconazole (CYP3A4 inhibitor). If concomitant use is required, monitor for signs or symptoms of increased or prolonged pharmacologic effects of haloperidol and reduce haloperidol dosage if necessary1.
Why it happens (mechanism)
Inhibition of CYP3A4-mediated metabolism of haloperidol
Literature reports
3 reports — tap to read
a) Increased QTc has been observed when haloperidol was given concomitantly with ketoconazole (CYP3A4 inhibitor) 400 mg/day 1.
b) The effect of nefazodone on the pharmacokinetics and pharmacodynamics of haloperidol was studied in 12 healthy male patients. Nefazodone 200 mg every 12 hours had a slight effect on the pharmacokinetics of a single dose of haloperidol 5 mg. The average AUC, highest concentration, and 12-hour concentration of haloperidol were increased 36%, 13%, and 37%, respectively. Only the effect on the AUC reached statistical significance. The pharmacodynamics of haloperidol were not effected by nefazodone consistently 2.
c) A single dose of haloperidol administered with steady-state nefazodone decreased haloperidol clearance. Pharmacodynamic effects of haloperidol were not significantly altered 3.
Common questions
Can I take Istradefylline and Haloperidol together?
Increased haloperidol exposure and an increased risk of haloperidol-related adverse events, including QTc interval prolongation Always confirm with your pharmacist or prescriber before making any change.
How serious is the Istradefylline and Haloperidol 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 Istradefylline or Haloperidol 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)
- Product Information: HALDOL(R) Decanoate 100 intramuscular injection, haloperidol decanoate intramuscular injection. Janssen Pharmaceuticals Inc (per FDA), Titusville, NJ, 2025.
- Barbhaiya RH, Shukla UA, Greene DS, et al: Investigation of pharmacokinetic and pharmacodynamic interactions after coadministration of nefazodone and haloperidol. J Clin Psychopharmacol 1996; 16:26-34. PubMed
- DeVane CL: Nefazodone--pharmacology and efficacy of a new antidepressant agent: formulary considerations. P and T 1995; 20:363-374.
Keep reading about Haloperidol
Keep reading about Istradefylline
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