Amantadine Risks, Warnings, and Complications

OVERDOSE: An overdose of amantadine can be fatal. This has been reported at doses of 1 gram. Overdose is more likely in people with kidney problems because amantadine is cleared from the body by the kidneys. In people with reduced kidney function, the medicine can build up in the body and lead to an overdose. Do not take more amantadine than prescribed. Before starting amantadine, tell your doctor if you have kidney problems.

SUICIDAL THOUGHTS OR BEHAVIOR: People who take amantadine, especially for the flu, have been reported to have suicidal ideation (thinking, planning, or attempting to harm or kill themselves). It is unclear why this occurs. However, the risk is higher in people with pre-existing mental illness or substance abuse problems. Tell your doctor right away if you notice any unusual behaviors, sudden changes in mood or personality, hallucinations, or paranoia while on amantadine.

EXCESSIVE SLEEPINESS: Medications that raise dopamine levels, including amantadine and other Parkinson’s medications like carbidopa/levodopa, can make you fall asleep suddenly, even during activities. Do not drive or do anything that requires your full attention until you know how amantadine affects you. There is a greater risk of this happening in people with a sleep disorder and those who are on other drugs that also cause drowsiness. Let your healthcare provider know if you find yourself feeling very sleepy during the daytime or falling asleep during activities.

PSYCHOTIC BEHAVIOR: Amantadine and other medications that increase dopamine levels in the brain can cause changes in thinking and behavior, including hallucinations, paranoia, delusions, uneasiness, confusion, aggression, trouble sleeping, abnormal dreams, and a reduced awareness of surroundings. These symptoms are more likely to occur shortly after starting amantadine and after dose adjustments. Talk to your doctor about the risks of taking amantadine if you have a history of mental health conditions. Certain medications prescribed for mental illnesses, such as haloperidol (Haldol) and perphenazine, can make Parkinson's disease worse and affect how amantadine works.

NEUROLEPTIC MALIGNANT SYNDROME: Rarely, suddenly stopping or lowering the dose of amantadine can lead to serious side effects such as neuroleptic malignant syndrome (NMS). This is a potentially life-threatening condition caused by certain mental health medications. Symptoms of NMS include very high fevers, confusion, irregular heartbeat, muscle stiffness, sweating, and blood pressure changes. NMS can be treated if it is diagnosed early. Do not stop taking amantadine or lower your dose without talking to your doctor. Your provider will tell you how to come off amantadine safely. 

DIFFICULTY IN CONTROLLING URGES: Amantadine and other medications for Parkinson’s disease can cause behavior changes, including increased sexual urges and other intense urges to gamble, binge eat, or spend money. Tell your doctor if you notice any such urges. You may not be aware you have these urges. People in your household should know what to look out for. Your healthcare provider will also ask about such behaviors at follow-up visits. 

CONGESTIVE HEART FAILURE: A small number of people can develop heart failure on amantadine. The risk is higher in people with a history of congestive heart failure or peripheral edema (swelling in the arms or legs). Tell your doctor if you develop swelling in any part of your body or shortness of breath while on amantadine.

SEIZURES: Amantadine can increase the risk of seizures in people who have had seizures before or are currently taking anti-seizure medications. Stop taking amantadine and call your doctor or seek emergency medical help if you have a seizure while on amantadine. 

KIDNEY DISEASE: The kidneys clear amantadine from the body. In older adults (age 65 years and above) and in people with a history of reduced kidney function, amantadine can build up in the body. This can increase the risk of side effects and overdose. Tell your healthcare professional if you have kidney problems. They will likely prescribe a lower dose of amantadine to lower your risk.

LIVER PROBLEMS: Rarely, amantadine can cause liver problems. The risk is higher in people with a history of liver disease. Before starting amantadine, give a complete medical history to your healthcare professional, including any history of liver problems.

SKIN CANCER: People with Parkinson's disease are at a higher risk of developing skin cancer. Tell your doctor if you notice any new or unusual skin growths or changes in a mole. Your provider may recommend regular skin examinations.