When is ketamine used to treat depression?

Ketamine infusion is effective for what is known as treatment resistant depression (TRD).  Treatment resistant depression is defined as depression which has not responded to the usual treatment consisting of selective serotonin reuptake inhibitors (SSRIs) along with talk therapy.  In the past, when depression persisted despite an adequate trial of these treatments, the only option was electroshock treatment.  Many studies have now shown that ketamine infusion is as effective as electroshock without all the associated side effects.  It is well-known that electroshock therapy can result in amnesia even for well-established memories as well as inhibit the development of new memories.  Ketamine infusion does not suffer from this problem.  There are other more subtle cognitive impairments associated with electroshock, which limits it use to the most extreme cases.  Because ketamine infusion is not associated with cognitive impairment, and because it is easier to administer and less costly, it can be used to treat people in whom electroshock would be undesirable.  Experience shows that it may even be the majority of cases which are treatment resistant and at the same time too mild to warrant electroshock.  Thus ketamine infusion is likely to change the treatment of depression dramatically.  The many people for whom standard therapy does not work but who do not want to undergo electroshock therapy now have an option.