Amantadine hydrochloride is primarily used in the treatment of Parkinson's disease and certain types of influenza. In Parkinson's disease, it helps to alleviate symptoms such as stiffness, tremors, and difficulty in movement by increasing dopamine release in the brain. It is also effective in managing drug-induced extrapyramidal symptoms, which are side effects of antipsychotic medications. For influenza, particularly influenza A, it acts as an antiviral agent by inhibiting the replication of the virus. Additionally, it is sometimes prescribed for fatigue management in patients with multiple sclerosis. Its use requires careful monitoring due to potential side effects and interactions with other medications.