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Osmolex ER Side Effects

Generic name: amantadine

Medically reviewed by Last updated on Mar 19, 2023.

Note: This document contains side effect information about amantadine. Some dosage forms listed on this page may not apply to the brand name Osmolex ER.

Applies to amantadine: oral capsule, oral capsule extended release, oral capsule liquid filled, oral solution, oral syrup, oral tablet, oral tablet extended release.

Serious side effects of Osmolex ER

Along with its needed effects, amantadine (the active ingredient contained in Osmolex ER) 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 amantadine:

More common

  • Bladder pain
  • bloody or cloudy urine
  • blurred vision
  • confusion
  • difficult, burning, or painful urination
  • dizziness or lightheadedness
  • fainting
  • falls
  • frequent urge to urinate
  • lower back or side pain
  • seeing, hearing, or feeling things that are not there
  • swelling of the hands, feet, or lower legs

Less common

  • Inability to move the eyes
  • increased blinking or spasms of the eyelid
  • muscle spasm
  • sticking out of the tongue
  • trouble breathing, speaking, or swallowing
  • uncontrolled twisting movements of the neck, trunk, arms, or legs
  • unusual facial expressions


  • Chills
  • decreased vision or any change in vision
  • difficulty in coordination
  • fever
  • increased blood pressure
  • increase in body movements
  • irritation and swelling of the eye
  • loss of memory
  • mental depression
  • seizures
  • severe mood or mental changes
  • skin rash
  • slurred speech
  • sore throat
  • thoughts of suicide or attempts at suicide

Other side effects of Osmolex ER

Some side effects of amantadine 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

Less common

  • Blindness
  • blurred vision
  • constipation
  • decrease in sexual desire
  • decreased vision
  • diarrhea
  • drowsiness
  • dry eyes
  • dryness of the mouth, nose, and throat
  • false sense of well-being
  • joint swelling
  • unusual tiredness or weakness
  • vomiting

For Healthcare Professionals

Applies to amantadine: compounding powder, oral capsule, oral capsule extended release, oral syrup, oral tablet, oral tablet extended release.


The more commonly reported adverse reactions have included nausea, dizziness/lightheadedness, and insomnia.[Ref]

Nervous system

Common (1% to 10%): Dizziness/lightheadedness, ataxia, headache, somnolence, dystonia

Uncommon (0.1% to 1%): Weakness, slurred speech, hyperkinesia

Rare (less than 0.1%): Convulsion

Frequency not reported: Falling asleep during activities of daily living, withdrawal-emergent hyperpyrexia (a syndrome resembling neuroleptic malignant syndrome)

Postmarketing reports: Coma, delirium, hypokinesia, involuntary muscle contractions, gait abnormalities, paresthesia, EEG changes, tremor[Ref]


Very common (10% or more): Hallucinations (up to 21%)

Common (1% to 10%): Insomnia, depression, anxiety, irritability, hallucinations, confusion, nervousness, abnormal dreams, agitation

Uncommon (0.1% to 1%): Psychosis, euphoria, abnormal thinking, amnesia

Rare (less than 0.1%): Suicide attempt, suicide, suicidal ideation

Postmarketing reports: Stupor, delusions, aggressive behavior, paranoid reaction, manic reaction, pathological gambling, increased libido including hypersexuality, and impulse control symptoms[Ref]


Very common (10% or more): Dry mouth (up to 16%); constipation (up to 13%)

Common (1% to 10%): Nausea, anorexia, diarrhea, decreased appetite

Uncommon (0.1% to 1%): Vomiting

Postmarketing reports: Dysphagia[Ref]


Very common (10% or more): Peripheral edema (up to 16%), orthostatic hypotension (up to 13%)

Uncommon (0.1% to 1%): Congestive heart failure, hypertension

Postmarketing reports: Cardiac arrest, arrhythmias including malignant arrhythmias, hypotension, and tachycardia[Ref]


Common (1% to 10%): Dry eye, cataract, blurred vision

Uncommon (0.1% to 1%): Visual disturbance, punctate subeithelial or other corneal opacity, corneal edema, decreased visual acuity, sensitivity to light, optic nerve palsy

Rare (less than 0.1%): Oculogyric episodes

Postmarketing reports: Keratitis, mydriasis[Ref]


Very common (10% or more): Fall (up to 13%)

Common (1% to 10%): Fatigue, contusions

Frequency not reported: Death

Postmarketing reports: Fever[Ref]

Deaths have been reported from overdose with the lowest reported acute lethal dose as 1 gram. Drug overdose has resulted in cardiac, respiratory, renal, or CNS toxicity. Deaths have been reported in patients with renal impairment and attributed to drug accumulation.[Ref]


Common (1% to 10%): Dry nose, cough

Uncommon (0.1% to 1%): Dyspnea

Postmarketing reports: Acute respiratory failure, pulmonary edema, tachypnea[Ref]


Rare (less than 0.1%): Leukopenia, neutropenia

Postmarketing reports: Leukocytosis, agranulocytosis[Ref]


Common (1% to 10%): Livedo reticularis, pigmentation disorder

Uncommon (0.1% to 1%): Skin rash

Rare (less than 0.1%): Eczematoid dermatitis

Postmarketing reports: Pruritus, diaphoresis[Ref]


Postmarketing reports: Allergic reactions including anaphylactic reactions[Ref]


Common (1% to 10%): Urinary tract infection, benign prostatic hyperplasia

Uncommon (0.1% to 1%): Urinary retention, decreased libido[Ref]


Postmarketing reports: Elevated: CPK, BUN, serum creatinine[Ref]


Rare (less than 0.1%): Reversible liver enzyme elevations

Postmarketing reports: Elevated: alkaline phosphatase, LDH, bilirubin, GGT, SGOT, and SGPT[Ref]


Common (1% to 10%): Joint swelling, muscle spasms[Ref]

Frequently asked questions


1. "Product Information. Symmetrel (amantadine)." DuPont Pharmaceuticals (2002):

2. "Product Information. Gocovri (amantadine)." Adamas Pharmaceuticals Inc. (2018):

3. "Product Information. Amantadine Hydrochloride (amantadine)." Sandoz Inc (2018):

4. Smith EJ "Amantadine-induced psychosis in a young healthy patient." Am J Psychiatry 165 (2008): 1613

5. Michalski LS, Hantsch Bardsley C, Holt DR, Milner JE, Hou SH "Altered mental status in a transplant patient. Amantadine toxicity." Kidney Int 75 (2009): 243-4

6. "Antiviral drugs for influenza." Med Lett Drugs Ther 51 (2009): 89-92

7. Kataoka H, Ueno S "Dropped head associated with amantadine in Parkinson disease." Clin Neuropharmacol 34 (2011): 48-9

8. Beal E "Parkinson disease: Amantadine administration is associated with impulse control disorders in PD." Nat Rev Neurol 7 (2011): 62

9. Salgado JC, Gutknecht DR "A reticular rash." Am J Med 119 (2006): 577-8

10. Alonso Navarro H, Sanz-Aiz A, Izquierdo L, Jimenez Jimenez FJ "Syndrome of Inappropriate Antidiuretic Hormone Secretion Possibly Associated With Amantadine Therapy in Parkinson Disease." Clin Neuropharmacol 32 (2009): 167-168

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.