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Istradefylline Side Effects

Medically reviewed by Last updated on Oct 14, 2022.

Applies to istradefylline: oral tablet.

Serious side effects of Istradefylline

Along with its needed effects, istradefylline may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur while taking istradefylline:

More common

  • Seeing, hearing, or feeling things that are not there
  • twitching, twisting, uncontrolled repetitive movements of tongue, lips, face, arms, or legs

Less common

  • Actions that are out of control
  • anxiety
  • attack, assault, force
  • confusion
  • confusion as to time, place, or person
  • delusions of persecution, mistrust, suspiciousness, or combativeness
  • dry mouth
  • false beliefs that cannot be changed by facts
  • hyperventilation
  • increased sexual urges
  • irregular heartbeats
  • irritability
  • restlessness
  • shaking
  • shortness of breath
  • talking, feeling, and acting with excitement
  • trouble sleeping
  • unusual excitement, nervousness, or restlessness

Other side effects of Istradefylline

Some side effects of istradefylline may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects.

Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

More common

  • Difficulty having a bowel movement (stool)
  • nausea

Less common

For Healthcare Professionals

Applies to istradefylline: oral tablet.


The most commonly reported adverse reactions have included dyskinesia, dizziness, constipation, nausea, hallucinations, and insomnia.[Ref]

Nervous system

Across clinical trials, dyskinesia occurred in 15% of patients receiving 20 mg once a day and 17% of patients receiving 40 mg once a day (compared to 8% for placebo); 1% of patients discontinued treatment because of dyskinesia.

Very common (10% or more): Dyskinesia (up to 17%)

Common (1% to 10%): Dizziness


Common (1% to 10%): Constipation, nausea


Common (1% to 10%): Rash


Common (1% to 10%): Decreased appetite, increased blood glucose


Common (1% to 10%): Blood alkaline phosphatase increased


Common (1% to 10%): Upper respiratory tract inflammation


Common (1% to 10%): Blood urea increased


Common (1% to 10%): Hallucinations, abnormal thinking and behavior, insomnia

Rare (less than 0.1%): Impulse control disorder

Postmarketing reports: Increased libido

Across clinical trials, hallucinations occurred in 2% of patients receiving 20 mg once a day and 6% of patients receiving 40 mg once a day (compared to 3% for placebo); 1% of patients discontinued treatment because of hallucinations. Across clinical trials, abnormal thinking and behavior (paranoid ideation, delusions, confusion, mania, disorientation, aggressive behavior, agitation, or delirium) occurred in 1% of patients receiving 20 mg once a day and 2% of patients receiving 40 mg once a day (compared to 1% for placebo). Across clinical trials, 1 patient taking 40 mg/day reported an impulse control disorder. There were no reports in the patients taking 20 mg/day or placebo.


1. "Product Information. Nourianz (istradefylline)." Kyowa Kirin, Inc (2019):

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Some side effects may not be reported. You may report them to the FDA.