The participants in the traditional Chinese medicine health preservation group will attend six traditional Chinese medicine health preservation courses (2h each per one, for 6 weeks) to learn and experience traditional Chinese medicine health preservation from a registered traditional Chinese medicine practitioner in a classroom at the School Nursing, the Hong Kong Polytechnic University.

Each class will be conducted in a small group of 4 to 6 participants to enhance interaction and ensure the quality of teaching. Participants will then practice traditional Chinese medicine health preservation at home for 6 weeks.

Participants in the waitlist control group will receive usual care during the 6-week waitlist period of intervention, and 6-week waitlist period of follow-up. After the follow-up assessment, they will be provided an equivalent traditional Chinese medicine health preservation for depression.

The traditional Chinese medicine health preservation intervention for depression was developed based on a previous systematic review and meta-analysis of Traditional Chinese medicine based integrated health interventions for depression, traditional Chinese medicine health preservation textbooks, clinical practice guidelines related to traditional Chinese medicine health preservation and traditional Chinese medicine treatment for depression. The content and structure of traditional Chinese medicine health preservation for depression was achieved among Hong Kong traditional Chinese medicine experts via a Delphi study.

The PHQ-9, a self-rated questionnaire to assess the presence and severity of depressive symptoms of an individual during the last 2 weeks on a scale of 0 (not at all) to 3 (nearly every day), with a total score ranging from 0 to 27. A higher score indicates a higher severity of depression symptoms.

The GAD-7 is a four-point Likert scale for identifying probable cases of GAD and assess the severity of symptoms of GAD for the past 2 weeks. The total score of GAD-7 varies from 0 to 21, and responses include "nearly every day," "more than half the days," "several days", and "not at all". The cutoff point of 5, 10, and 15 of GAD-7 might be interpreted as showing mild, moderate, and severe levels of anxiety. Higher scores indicate more severe GAD symptoms.

The CEQ is a self-reported scale with 6 items and two subscales of treatment credibility and outcome expectancy to measure the participants' treatment credibility and outcome expectancy for improvement. The final scoring of the CEQ is computed by the sum of the items composing each subscale, with a higher quotation referring to higher treatment credibility and outcome expectation.

The CEQ taps on participants' affective and cognitive evaluations of treatment satisfaction, credibility, and expectation. The subscale of credibility assesses beliefs about the treatment strength. The expectancy subscale assesses how participants perceive their symptoms will improve during the intervention period.