Lycium barbarum, a traditional Chinese herbal medicine, is a commonly used herb in the traditional Chinese pharmacopoeia . Its main active ingredient, lycium barbarum polysaccharide (LBP), is reported to have neuroprotective effects. Animal studies suggested that LBP has neuroprotective effect on optic ganglion cells. In animal models of depression, LBP can improve depressive symptom by improving synaptic plasticity. However, its clinical effect remains to be studied. We will conduct a 6-week double-blind, randomized, placebo-con-trolled trial in people with subthreshold depression.The purpose of this clinical trial is to investigate the efficacy of LBP in people with subthreshold depression.

Inclusion Criteria:

1. 15-25 scores in the Beck Depression Rating Scale (BDI- II)
2. There is no contraindication of taking LBP.

Exclusion Criteria:

1. Current treatment for a mental health problem from a mental health professional
2. Current and lifetime history of psychiatric disorders (e.g major depressive disorder, as ascertained by CIDI
3. Systemic disease requiring regular medication.
4. There are suicidal ideation, suicidal attempt, suicide behavior and attempted suicide.
5. Dislike of or allergy to goji berry
6. Hormone or Endocrine therapeutic drugs are being taken.
7. Long-term use of lycium chinensis in recent three months