This is a study on Parkinson's disease patients, referred to Tohid Hospital of Sanandaj City. The patients receive N-acetylcysteine for one year. The efficacy of the Drug is evaluated based on clinical interview, filling Unified Parkinson's Disease Rating Scale (UPDRS) questionnaire, and single-photon emission computerized tomography (SPECT) brain imaging. The only person who has not been blinded for the study is the supplier of the drug and placebo.

Inclusion criteria: Patient's informed consent Exclusion criteria: Having brain surgery within a year before the initiation of the intervention.

Medication group: receiving 1200 mg N-acetylcysteine per day, twice daily, each time 600 mg.

placebo group: receiving a placebo with similar appearance, color, odor, and taste like real medication.

This is a randomized double-blinded clinical trial. Randomization method is based on making blocks with size of 4 people, to divide participants into two groups: intervention group (A) and control group (B). So that, we divide all participants to four-sample blocks, and we allocate the block's samples equally between the two groups (e.g. ABAB). This pattern is the same in all blocks. Participants, clinical caregivers, outcome evaluators and data analyzers are not aware whether the therapeutic regimens include the drug or placebo. only the main researcher and pharmacist are aware of nature of therapeutic regimen based on codes given to the drug and placebo packages, earlier.

Inclusion Criteria:

• Patient's informed consent No brain surgery in the patient's post medical history

Exclusion Criteria:

• having brain surgery within a year before starting the treatment period