Often tests are done to rule out other conditions which resemble Parkinsons. Treatment is needed to correct the chemical imbalance. Drugs alleviate the symptoms but do not halt the progression of Parkinsons. As the symptoms increase, more medication is needed. While treatment does enable people to function better, it is not perfect and may cause side effects.
Ongoing research is focused on finding more effective treatments.
I must stress that not for nothing has PD been called a designer disease. No two of us have the same symptoms and everything I say will be true for some PWP but not for others. Even what is true for me to day may or may not be true tomorrow. Another thing to keep in mind is that in the early to middle stage of PD, medication can, and for most of us does, reduce the severity of symptoms, often dramatically. It is as the disease progresses through later middle stage into end stage that problems with symptoms and side effects start to occur.