Symmetrel Side Effects

Generic name: amantadine

Medically reviewed by Drugs.com. Last updated on Feb 4, 2025.

Note: This document provides detailed information about Symmetrel Side Effects associated with amantadine. Some dosage forms listed on this page may not apply specifically to the brand name Symmetrel.

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 Symmetrel

Along with its needed effects, amantadine (the active ingredient contained in Symmetrel) 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 side effects

• 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 side effects

• 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

Rare side effects

• 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 Symmetrel

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 side effects

• agitation
• anxiety
• difficulty concentrating
• dry mouth
• headache
• irritability
• loss of appetite
• nausea
• nervousness
• nightmares
• purplish red, net-like, or blotchy spots on the skin
• trouble with sleeping

Less common side effects

• 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 liquid, oral tablet, oral tablet extended release.

General adverse events

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]

Psychiatric

• 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]

Gastrointestinal

• 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]

Cardiovascular

• 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]

Ocular

• 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]

Other

• 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]

Respiratory

• Common (1% to 10%): Dry nose, cough
• Uncommon (0.1% to 1%): Dyspnea
• Postmarketing reports: Acute respiratory failure, pulmonary edema, tachypnea^[Ref]

Hematologic

• Rare (less than 0.1%): Leukopenia, neutropenia
• Postmarketing reports: Leukocytosis, agranulocytosis^[Ref]

Dermatologic

• 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]

Hypersensitivity

• Postmarketing reports: Allergic reactions including anaphylactic reactions^[Ref]

Genitourinary

• Common (1% to 10%): Urinary tract infection, benign prostatic hyperplasia
• Uncommon (0.1% to 1%): Urinary retention, decreased libido^[Ref]

Renal

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

Hepatic

• Rare (less than 0.1%): Reversible liver enzyme elevations
• Postmarketing reports: Elevated: alkaline phosphatase, LDH, bilirubin, GGT, SGOT, and SGPT^[Ref]

Musculoskeletal

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

Frequently asked questions

• What is the difference between Osmolex ER and Gocovri?
• What is Gocovri used to treat?
• Why should you not discontinue amantadine?
• How long does it take for amantadine to start working?
• Why was amantadine discontinued for flu?
• What symptoms does amantadine treat?
• What is Gocovri (amantadine) and how does it work?

Further information

Symmetrel side effects can vary depending on the individual. Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Note: Medication side effects may be underreported. If you are experiencing side effects that are not listed, submit a report to the FDA by following this guide.

Medical Disclaimer