What is Amantadine?
Amantadine is a medication primarily used to treat symptoms of Parkinson's disease, such as stiffness, tremors, and dyskinesia (uncontrolled movements) [1.5.2, 1.5.3, 1.5.6]. It can be prescribed alone or with other Parkinson's medications like levodopa/carbidopa [1.5.2]. By improving muscle control, it helps patients experience more normal body movements [1.5.3]. Additionally, amantadine is used to manage movement problems that are side effects of certain drugs [1.5.2, 1.5.8].
Historically, amantadine was also used as an antiviral agent to prevent and treat influenza A virus infections [1.5.2, 1.5.3]. However, due to widespread drug resistance, the Centers for Disease Control and Prevention (CDC) no longer recommends its use for this purpose [1.5.1]. Beyond its FDA-approved uses, clinicians have explored amantadine for off-label purposes, including managing fatigue in multiple sclerosis, chorea in Huntington's disease, and aiding recovery from traumatic brain injuries [1.5.1].
How Amantadine Works
The precise mechanism of action for amantadine's effects in Parkinson's disease is not fully understood [1.4.1]. It is believed to work by influencing several neurotransmitter systems in the brain. Data suggests it has direct and indirect effects on dopamine neurons, potentially increasing dopamine release and blocking its reuptake [1.4.1, 1.4.6]. This helps balance substances in the brain that control body movements and coordination [1.5.4]. More recent studies have also identified it as a weak, non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist, which may contribute to its effectiveness, particularly in reducing levodopa-induced dyskinesia [1.4.1, 1.4.3]. Its antiviral action involved interfering with a viral protein (M2) to prevent the virus from replicating inside host cells [1.4.4].
Does Amantadine Cause Diarrhea?
Yes, amantadine can cause diarrhea, but it is considered a less common side effect [1.3.1]. According to drug information labels, diarrhea is reported in 1% to 5% of patients taking the medication [1.2.5, 1.3.7]. It is listed alongside other less frequent gastrointestinal issues like anorexia (loss of appetite), dry mouth, and constipation [1.2.5]. Some sources classify it as a rare side effect [1.2.6].
Mild gastrointestinal side effects, including diarrhea or gas, may occur when first starting the medication and can resolve over time [1.2.1]. While nausea is a more frequently reported gastrointestinal issue (affecting 5-10% of users), diarrhea remains a possibility that patients should be aware of [1.3.2, 1.2.5].
Managing Gastrointestinal and Other Side Effects
If you experience persistent or bothersome side effects like diarrhea, it is important to speak with your healthcare provider [1.6.4]. Mild side effects often go away after a few days or weeks as your body adjusts to the medication [1.6.4]. For gastrointestinal issues like constipation, which is more common than diarrhea with amantadine, staying hydrated and consuming enough fiber can help [1.6.1].
It is crucial not to stop taking amantadine suddenly without consulting your doctor, as this can lead to serious withdrawal symptoms, including high fever, confusion, and severe muscle stiffness, a condition resembling neuroleptic malignant syndrome (NMS) [1.5.2, 1.6.3]. Your doctor can help you safely discontinue the medication by gradually reducing the dose over several weeks [1.6.1, 1.6.5].
General tips for managing side effects include:
- Dizziness/Lightheadedness: Get up slowly from a sitting or lying position [1.6.1].
- Drowsiness: Avoid driving or operating machinery until you know how the medication affects you. Alcohol can worsen this effect and should be avoided [1.6.1, 1.6.2].
- Dry Mouth: Chewing sugarless gum, sucking on hard candy, and drinking plenty of water can provide relief [1.6.7].
Side Effect Profile: A Comparison
Amantadine has a wide range of potential side effects, from common and mild to rare and serious.
| Common Side Effects (5-10%) | Less Common Side Effects (1-5%) | Rare/Serious Side Effects (<1%) |
|---|---|---|
| Nausea [1.2.5] | Depression, anxiety [1.2.5] | Seizures [1.3.1] |
| Dizziness/Lightheadedness [1.2.5] | Hallucinations [1.2.5] | Suicidal thoughts or attempts [1.2.5] |
| Insomnia (trouble sleeping) [1.2.5] | Confusion [1.2.5] | Neuroleptic Malignant Syndrome (NMS) [1.2.5, 1.3.2] |
| Dry Mouth [1.2.5] | Loss of appetite (anorexia) [1.2.5] | Congestive heart failure [1.2.5] |
| Constipation [1.3.6] | Dry mouth, constipation [1.2.5] | Psychosis [1.2.5] |
| Livedo reticularis (skin discoloration) [1.3.1] | Ataxia (impaired coordination) [1.2.5] | Leukopenia/Neutropenia (low white blood cell count) [1.2.5] |
| Peripheral edema (swelling) [1.2.5] | Headache, somnolence (drowsiness) [1.2.5] | Corneal edema or opacity [1.2.5] |
| Orthostatic hypotension [1.2.5] | Dream abnormalities, agitation [1.2.5] | Allergic reactions [1.2.5] |
| Diarrhea [1.2.5] |
Conclusion
To answer the question, 'Does amantadine cause diarrhea?', the evidence shows that while it is a recognized side effect, it is not a common one. It occurs in a minority of patients, often at the beginning of treatment, and may resolve on its own. The more prevalent gastrointestinal side effects are nausea and constipation. As with any medication, it is vital for patients to maintain open communication with their healthcare provider to monitor for and manage any adverse effects. Any persistent or severe symptoms, including diarrhea, should be reported to a doctor to ensure safe and effective treatment.
For more detailed information, you can consult the official drug information on DailyMed provided by the National Library of Medicine: Amantadine Hydrochloride Capsules, USP Rx only
