This clinical study is a double-blind, randomized, placebo-controlled trial to investigate the effects of melatonin on the sleep disturbance symptoms of Parkinson's disease patients, symptoms which have a significant impact on the quality of life of these patients.

After selecting patients who satisfied the inclusion criteria and were not disqualified by the exclusion criteria, through a double-blind procedure the patients are directed to orally take either the investigational drug melatonin or a placebo(allocation ratio 1:1) for 4 weeks, once daily, before going to sleep. The evaluation of efficacy and safety is performed at the first baseline and immediately after administering the drug for 4 weeks.

Inclusion Criteria:

1. Patients who meet the clinical criteria for idiopathic Parkinson's disease (United Kingdom Parkinson's Disease Brain Bank Criteria)
2. Patients who complain of sleep disturbances such as insomnia, REM sleep behavior disorder, excessive daytime sleepiness (EDS), etc.
3. Patients who have received drug treatment for at least 6 months since their diagnosis
4. Male or female patient aged 55 or older
5. Patients who have given voluntary consent after understanding the content of the clinical trial (in the case of elderly patients aged 70 or older, consent must be received from both the subject and the his or her legal representative)

Exclusion Criteria:

1. Patients with a serious cognitive disorder, behavioral disorder, or mental illness

2. Patients with a serious medical disease

   • Patients who concomitantly suffer from severe renal impairment, convulsions, stomach ulcers, moderate or more severe liver disease
   • Patients with un-controlled high blood pressure or diabetes

3. Patients who have taken another investigational products within 4 weeks prior to being enrolled in this clinical trial, or patients who are pregnant or breastfeeding

4. Patients who have a history of hypersensitivity to the investigational products or a drug similar in component or who have had heavy metal poisoning