This article I found very interesting and I do believe that ayahuasca can help with depression, and is one of the reasons I would like to try it myself. Reports I have read indicate that ayahuasca, rather than obscuring reality from the user like other mainstream drugs do, forces the individual to confront their insecurities and deal with them accordingly. I have read many reports of the transformative nature of an ayahuasca experience where the failings or faults of an individual are brought to the fore and the individual is obliged to confront them, some of which the individual wasn't even aware of and was hidden in the subconscious.
We all have failings and faults but with depression the inner voice constantly reminds the individual of those insecurities. If ayahuasca forces the individual to deal with insecurities and process them accordingly the inner voice would focus on positive things rather than the negative – this article has a lot of parallels with the treatment of prisoners article someone recently posted.