In cases of moderate depression, supplementation with a fairly high dose of B vitamins accelerates the recovery process. This is suggested by a somewhat older American human study published in ISRN Psychiatry.

Study
In 2013, psychiatrists at the University of Miami published a study involving 60 adults with moderate depression. Some of the participants used antidepressants, anti-anxiety medications, or sleeping pills.

The researchers divided the participants into two groups: an experimental group and a placebo group. There were no statistically significant differences between the medication use in the two groups.

Every day for 60 days, participants in the experimental group received half a teaspoon of a liquid containing B vitamins derived from a probiotic culture. Participants in a control group received a placebo without any vitamins.

The researchers used a supplement marketed as Max Stress B. The composition is shown in the table below. Click on it for a larger version.

The doses of folate and vitamin B12, in particular, were extremely high—but as far as we know, they are not toxic.

Max Stress B is a product of Premier Research Labs, a company that sponsored the study.

Results
The researchers assessed depression severity using the Beck Depression Inventory, a standardized questionnaire. Before the trial began, participants' scores fell at the lower end of the moderate depression range.

During supplementation, their scores declined into the mild range. The decrease occurred in both groups, but appeared somewhat more convincing in the experimental group.