Inclusion Criteria:
* Male and female adults at the age of ≥ 55 to ≤ 85 at the time of informed consent
* Patients diagnosed according to the NIA-AA 2024 Criteria for Diagnosis with Mild Cognitive Impairment (MCI) or diagnosed with mild Alzheimer's disease
* CDR-GS 0.5-1.0 at Screening
* MMSE ≥ 20 at Screening
* Amyloid-positive at amyloid PET scan
* Patients who are capable of understanding information provided and can voluntarily sign written informed consent form
Exclusion Criteria:
* Subjects diagnosed with cognitive impairment due to causes other than substrate causes such as brain lesions, psychiatric disorders, or Alzheimer's disease (e.g., stroke, Parkinson's disease, Lewy body disease, vascular dementia)
* Subjects with any of the following cardiovascular diseases at Screening
\* Cerebrovascular disease within the past 6 months (cerebral infarction, cerebral hemorrhage, transient ischemic attack, etc.)
* Myocardial infarction or unstable angina pectoris within the past 6 months
* New York Heart Association (NYHA) Class II congestive heart failure
* QTcF ≥450 msec or clinically significant electrocardiogram (ECG) abnormalities
* Patients with malignant tumors
* Patients with medical conditions that can affect cognitive decline such as hypothyroidism, vitamin B12 or folate deficiency, niacin deficiency, etc.
* Patients with a history of alcohol related disorders within the past 6 months
* Patients with a positive HIV antibody test result at Screening
* Patients with a positive HBs antigen or HCV antibody test at Screening
* Patients with active bacterial infections who have received antibiotics within 7 days prior to Screening.
* Patients with a history of hypersensitivities to any of the components of investigational product
* Patients who have been hospitalized or treated for suicidal behavior within 5 years prior to Screening or whose C-SSRS results at Screening indicate serious suicidal ideation or behavior
* Patients who have received treatment for Alzheimer's disease (e.g., Lecanemab) within 6 months prior to Screening
* Patients expected to require the administration of a long-acting benzodiazepine (BDZ) for the treatment of sleep disorders at Screening
* Any of the following laboratory test values at Screening:
* Serum Creatinine \>1.5×ULN or eGFR (MDRD) \<40 mL/min/1.73 m2
* Any of the following: AST, ALT \>3×ULN, or Total bilirubin \>2xULN
* Women who test positive for pregnancy at Screening, or women and men of childbearing potential who are planning to become pregnant, or who do not agree to use adequate contraception\* during the study and for 4 weeks after the end of study drug administration
\*Adequate contraception: complete abstinence, hormonal contraceptives with no known drug interactions \[Levonorgestrel intrauterine system (IUS) (Mirena), Medroxyprogesterone\], surgical sterilization (including vasectomy, bilateral salpingectomy and ligation). However, intermittent abstinence (e.g., using ovulation timing, symptothermal method, or post-ovulation) or external ejaculation are not considered adequate contraception.
* Pregnant or lactating women or women who are tested positive for pregnancy at Screening
* Patients treated with other IP within 4 weeks prior to screening
* Patients who are considered ineligible for study participation for other reasons based on the judgment of the investigator
\[Extension Study\]
Inclusion Criteria:
* Patients who completed the 26-week visit in the Main Study
* Patients who provided written consent to participate in the Extension Study
Exclusion Criteria:
* Subjects who have dropped out of the Main Study
* Patients who, in the investigator's judgement, are not suitable for participation in Extension Study
* Any of the following laboratory test values at Baseline:
* Serum Creatinine \>1.5×ULN or eGFR (MDRD) \<40 mL/min/1.73 m2
* Any of the following: AST, ALT \>3×ULN, or Total bilirubin \>2xULN