First of all, you have to be aware that most studies cited are on animals, not humans. Applicability of that data for humans is limited.
Second, this molecule is interacting with all kinds of tissues thoughout the entire body. Its pharmacology is quite complicated, but it shows a lot of potential. In general. Its use for depression is not yet among the most promonent applications investigated.
Pisanti, S., et al., Cannabidiol: State of the art and new challenges for therapeutic applications, Pharmacology & Therapeutics (2017), DOI
In the case of schizophrenia:
These findings suggest that CBD has beneficial effects in patients with schizophrenia. As CBD’s effects do not appear to depend on dopamine receptor antagonism, this agent may represent a new class of treatment for the disorder.
Philip McGuire: "Cannabidiol (CBD) as an Adjunctive Therapy in Schizophrenia: A Multicenter Randomized Controlled Trial", American Journal of Psychoiatry, Volume 175, Issue 3, March 01, 2018, Pages 225-231. DOI
The above should not read as "it safe to experiment with this in schizophrenia". But it is a significant finding as
So far, much of the evidence regarding the antipsychotic effects of CBD has come from studies with animals or healthy participants.
There have only been a handful of double-blind trials so far reported that have included patients with psychosis.
The others (Leweke et al. 2012, Boggs et al. 2018) featured smaller sample sizes (N=42 and N=36 respectively) and lower doses (800mg and 600mg per day respectively).
Leweke et al. compared CBD to Amisulpride, and found both had a similar effect on psychotic symptoms but CBD had fewer side-effects.
Boggs et al. also tested CBD against placebo as an adjunct to existing antipsychotic treatment, but found no statistically significant effect after 6 weeks.
Boggs D., Surti T., Gupta A., et al. (2018). The effects of cannabidiol (CBD) on cognition and symptoms in outpatients with chronic schizophrenia a randomized placebo controlled trial. Psychopharmacology. 235, 1923-1932. [Abstract]
Bridgeman M, Abazia D. (2017) Medicinal cannabis: History, pharmacology, and implications for the acute care setting. Pharm. Ther., 42, 180–188.
Fakhoury, M. (2016) Could cannabidiol be used as an alternative to antipsychotics? Journal of Psychiatric Research , Volume 80 , 14 – 21. [Abstract]
Gage, S. H., Hickman, M., & Zammit, S. (2016). Association Between Cannabis and Psychosis: Epidemiologic Evidence (PDF). Biological Psychiatry, 79(7), 549-556.
Lim, K., See, Y.M., Lee, J. (2017) A systematic review of the effectiveness of medical cannabis for psychiatric, movement and neurodegenerative disorders. Clin Psychopharmacol Neurosci.; 15:301–312.
Mücke M, Phillips T, Radbruch L, et al. (2018) Cannabis-based medicines for chronic neuropathic pain in adults. Cochrane Database of Systematic Reviews, Issue 3. Art. No.: CD012182.
Nielsen S., Germanos R., Weier M. et al. (2018). The Use of Cannabis and Cannabinoids in Treating Symptoms of Multiple Sclerosis: a Systematic Review of Reviews. Current Neurology and Neuroscience Reports. 18: 8. [PubMed abstract]
O’Connell, B. K., Gloss, D. & Devinsky, O. (2017) Cannabinoids in treatment-resistant epilepsy: a review. Epilepsy Behav. 70, 341–348. [PubMed abstract]
Rong C, Lee Y, Carmona NE, et al. Cannabidiol in medical marijuana: research vistas and potential opportunities. Pharmacol Res. 2017;121:213–8. [PubMed abstract]
Luke Sheridan Rains: "Is Cannabidiol (CBD) an effective antipsychotic?", 24 Aug 2018