Many hypnotherapists are uncomfortable using hypnosis with clinically depressed clients.
This may be because it is generally considered to be too passive a treatment and unlikely to help the client get out of depression. The preference seeems to be for a more active type of therapy like cognitive or behavioural therapies.
Perhaps the best use of hypnosis is to use it in conjunction with these therapies?
A good author to check out in regard to hypnosis and depression is Dr Michael Yapko who has written " Hypnosis in the treatment of depressions " and other titles on this matter.
www.hypnosis-london.co.uk