Final answer:
The first-line therapy for patients with Parkinson's disease is L-DOPA, which is converted into dopamine by neurons in the brain to increase dopamine levels and compensate for the loss of dopaminergic neurons.
Step-by-step explanation:
The first-line therapy for patients with Parkinson's disease is L-DOPA. L-DOPA is a chemical that is converted into dopamine by neurons in the brain, increasing dopamine neurotransmission and compensating for the loss of dopaminergic neurons in the substantia nigra. Other drugs that inhibit the enzyme breaking down dopamine can also be used.