The investigators designed this double blind randomized controlled study and will recruit 120 patients 20 to 65 years old, with DSM-5 generalized anxiety disorder or unspecified anxiety disorder. After clinical symptoms and psychological evaluation and blood sampling, a semi-structural interview delivered by a psychiatrist will be established to confirm the DSM-5 diagnosis. The participants will be randomly assigned to the Lactobacillus paracasei PS23 psychotropic probiotic or placebo group. Blood and stool samples will be obtained after consent. The samples will be tested for biochemistry, inflammation index, cytokines, intestinal osmotic pressure, or gut permeability, and a Fitbit fitness watch will be given to measure changes in sleep.

This study aimed to recruit 120 subjects that meet the following inclusion criteria after the approval of the IRB. Those agreed to participate and signed the informed consent will be randomly divided into two groups of the Lactobacillus paracasei PS23 psychobiotics capsule and the placebo. Each group aims to recruit 60 people. The power analysis was conducted using effect size for outcomes of improvements in anxiety from previous studies. Based on a power of 80% and assuming a 30% dropout rate and an alpha level of 0.05, a sample of 120 participants (60 per group) will be required. All results will be analyzed using an intent-to-treat analysis based on treatment assignment, regardless of completion or not.

Inclusion Criteria:

1. Age 20~70 years old
2. Patients perceived that they had anxiety-related complaints, or with any type of anxiety disorders of adjustment disorders referred from the Departments of Psychiatry, Neurology, Internal Medicine, and Family Medicine in Mackay Memorial Hospital.
3. Adult GAD-7 ≥ 8 points (to screen for generalized anxiety disorder) or a DSM-5 diagnosis of generalized anxiety disorder (F41.1) or unspecified anxiety disorder (F41.9)
4. Those who are currently under the treatment of selective serotonin reuptake inhibitors (SSRI) will only be included if their SSRI treatment has been stable or has not been changed for 4 weeks.

Exclusion Criteria:

1. Have taken antibiotics or are receiving antibiotic treatment within one month.
2. Have used probiotic products in powder, capsule or tablet form within two weeks (excluding yogurt, Yakult and other related foods).
3. Patients who have undergone hepatobiliary gastrointestinal surgery (except for colorectal polypectomy and appendectomy).
4. Past or current patients with inflammatory bowel disease.
5. Those with a history of cancer.
6. Those who are allergic to lactic acid bacteria products.
7. Patients with severe depression (Patient Health Questionnaire-9 (PHQ-9) ≧ 20 points), or possible neurocognitive impairments (Mini-Mental States Examination (MMSE)<20), or those that had suicidal ideation noted on item 9 from PHQ-9.
8. Patients with chronic psychiatric diseases who are currently taking drugs to treat acute diseases, organic brain diseases, or newly diagnosed or changed drugs within one month.
9. Those who are receiving parenteral nutrition.
10. Those who are evaluated by the principal investigator to be unsuitable to participate in the research.