Reviewed on 2/2/2023

What Is istradefylline and How Does It Work?

Istradefylline is a prescription medication used for the treatment of Parkinson’s Disease. 

  • Istradefylline is available under the following different brand names: Nourianz

What Are Side Effects Associated with Using Istradefylline?

Common side effects of Istradefylline include:

  • Involuntary muscle movements,
  • Hallucinations,
  • Dizziness,
  • Nausea,
  • Constipation, and
  • Sleep problems (insomnia)

Serious side effects of Istradefylline include:

  • Hives,
  • Difficulty breathing,
  • Swelling of the face, lips, tongue, or throat,
  • Uncontrolled or involuntary muscle movements,65
  • Unusual thoughts or behavior,
  • Confusion,
  • Hallucinations,
  • Risk-taking behavior, and
  • Impulsive behavior

Rare side effects of Istradefylline include:

  • None 

Seek medical care or call 911 at once if you have the following serious side effects:

  • Severe headache, confusion, slurred speech, arm or leg weakness, trouble walking, loss of coordination, feeling unsteady, very stiff muscles, high fever, profuse sweating, or tremors;
  • Serious eye symptoms such as sudden vision loss, blurred vision, tunnel vision, eye pain or swelling, or seeing halos around lights;
  • Serious heart symptoms include fast, irregular, or pounding heartbeats; fluttering in the chest; shortness of breath; sudden dizziness, lightheadedness, or passing out. 

This is not a complete list of side effects and other serious side effects or health problems that may occur because of the use of this drug. Call your doctor for medical advice about serious side effects or adverse reactions. You may report side effects or health problems to FDA at 1-800-FDA-1088.

What Are the Dosages of Istradefylline?

Adult dosage


  • 20 mg
  • 40 mg

Parkinson Disease

Adult dosage

  • 20 mg orally once a day; may increase to a maximum of 40 mg orally once a day.
  • Initial dose titration is not required.

Dosage Considerations – Should be Given as Follows: 

  • See “Dosages”


Parkinson's disease is only seen in people of advanced age. See Answer

What Other Drugs Interact with Itradefylline?

If your medical doctor is using this medicine to treat your pain, your doctor or pharmacist may already be aware of any possible drug interactions and may be monitoring you for them. Do not start, stop, or change the dosage of any medicine before checking with your doctor, health care provider, or pharmacist first.

  • Istradefylline has severe interactions with no other drugs.
  • Istradefylline has serious interactions with at least 36 other drugs.
  • Istradefylline has moderate interactions with at least 368 other drugs.
  • Istradefylline has minor interactions with the following drugs:

This information does not contain all possible interactions or adverse effects. Visit the RxList Drug Interaction Checker for any drug interactions. Therefore, before using this product, tell your doctor or pharmacist about all your products. Keep a list of all your medications with you and share this information with your doctor and pharmacist. Check with your healthcare professional or doctor for additional medical advice, or if you have health questions or concerns.

What Are Warnings and Precautions for Istradefylline?


  • None

Effects of drug abuse

  • None

Short-Term Effects

  • See “What Are Side Effects Associated with Using Istradefylline?”

Long-Term Effects

  • See “What Are Side Effects Associated with Using Istradefylline?”


  • Coadministration with levodopa may cause dyskinesia or exacerbate preexisting dyskinesia; in clinical trials, dyskinesia incidence was higher in patients taking istradefylline compared with placebo
  • May exacerbate psychosis; patients with a major psychotic disorder should not be treated with istradefylline; consider dosage reduction or discontinuation if a patient develops hallucinations or psychotic behaviors while receiving therapy
  • Patients treated with istradefylline and above 1 medication(s) for PD (including levodopa) may experience intense urges to gamble, increased sexual urges, intense urges to spend money, binge or compulsive eating, and/or other intense urges, and the inability to control these urges; consider dose reduction or discontinuation
  • Based on animal studies, may cause fetal harm
  • Drug interaction overview
    • CYP inhibitors or inducers
      • Istradefylline is primarily metabolized by CYP3A4 and CYP1A1
      • Coadministration with strong CYP3A4 inhibitors: Not to exceed istradefylline 20 mg once a day
    • Strong CYP3A4 inducers: Avoid coadministration
      • Increase istradefylline dose with tobacco use equivalent to above 20 cigarettes/day
      • Istradefylline effect on other drugs
      • Istradefylline is both a weak CYP3A4 inhibitor and inducer; higher istradefylline doses (.e, 40 mg/day) may affect CYP3A4 substrates
      • Transporters: Istradefylline is a weak inhibitor for P-GP, BCRP, OATP1B1, OATP1B3, OAT1, OCT2, MATE1, and MATE2-K; higher istradefylline doses (. e, 40 mg/day) may affect P-GP substrates (.g, digoxin)

Pregnancy and Lactation

  • Data are unavailable regarding use in pregnant women
  • Based on animal studies, may cause fetal risk
  • Use during pregnancy is not recommended; advise women of childbearing potential to use contraception during treatment
  • Lactation
    • There are no data on the presence of human milk, its effects on breastfed infants, or its effects on milk production.
    • Present in the milk of lactating rats at concentrations up to 10 times that in maternal plasma.
    • Consider the developmental and health benefits of breastfeeding along with the clinical need for istradefylline, and any potential adverse effects on breastfed infants from istradefylline or the underlying maternal condition.


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