Amanatadine initially was an antiviral medication against influenza, but its main use now is as a type of pain reliever as it inhibits something called an NMDA receptor.
The NMDA receptor is a nervous system receptor that can bind to aspartate (or more specifically to N-methyl-D-aspartate) or glutamate to create chronic pain. Even worse, when glutamate or aspartate binds to this receptor, a stimulus that is normally not painful actually becomes painful.
By coincidence it was found to help the symptoms of Parkinson's disease. It may be used alone or in combination with levodopa or dopamine agonists. Amantadine reduces symptoms of fatigue, tremor and bradykinesia.
I was taking 2 Sinemet CR and 1 Sinemet 25/100, 12 Requip (2 mg) daily in the year of 2006 and to my surprise when added 3 Amantadine (100mg ) it caused reddish mottling on few part of my body and legs which was sideeffect of Amantadine and I apply Antiseptic cream to stop itchiness. I had stopped the medicine.
In general sideeffects of this medication may cause stomach upset, nausea, drowsiness, constipation, headache, dizziness, anxiety, or purplish-red blotchy spots on the skin during the first few days as your body adjusts to the medication. If these symptoms persist or become severe, inform your doctor promptly. Notify your doctor if you develop: slurred speech, shortness of breath, swelling of the ankles/feet, unusual fatigue, vision disturbances, difficulty urinating, skin rash, mental/mood changes (sometimes severe, including rare thoughts of suicide), muscle stiffness, uncontrolled muscle movements, unusual sweating, fast heartbeat, unexplained fever. If you notice other effects not listed above, contact your doctor or pharmacist.