Parkinson's disease is caused by a lack of dopamine in the brain. Dopamine is a neurotransmitter which conveys messages between neurons. A lack of dopamine causes tremors and impaired movement as well as non-motor symptoms.
Medical treatment focuses on restoring the balance of dopamine and falls under two main categories of dopamine replacement therapy and dopamine agonists. Like all medications they can cause undesirable side effects.
Usually the prescribing physician will be a neurologist and possibly a geriatrician. It's important to maintain clear communication with your treating physician and monitor for any side effects or changes in your condition.
Parkinson's Australia is a good source of information on medical treatments for this neurological condition.