A study carried out by the Institute of Psychiatry found that providing therapy for a person with depression and their partner was more successful than conventional drug treatment.
The study found that depressed people who went to a "couple" therapist were more likely to improve than those who were just prescribed drugs.
This form of therapy aims to help the depressed individual and their partner to gain new outlooks on the problems that face the depressed person.
They are encouraged to attach new, more positive meanings to the depressed person's behaviour and to experiment with new ways of relating to each other.
As part of the study, depressed individuals and their partners were randomly allocated to either a year of antidepressant treatment or to couple therapy sessions.
At the end of the year, both treatments were stopped and the depressed individuals were followed up for a second year to test whether either treatment helped to prevent the return of depression.
At the end of the first year, it was found that couple therapy was more effective in improving depression.
During the second year, without any treatment, the depressed individuals who had taken part in couple therapy remained less depressed than those who had taken antidepressant drugs.
Advantage
This, said the authors, showed that the advantage of couple therapy continued over a long period.
Professor Julian Leff, head of the social psychiatry section of the Institute of Psychiatry and author of the research, said the study suggested that primary care workers should be trained in couple therapy.
"We knew that depressed people who live with partners who are critical of them are more likely to suffer a return of their depression.
"But now we can show that the reverse is true, that a positive partner can lift a depressed partner out of their blues.
"We consider that our findings form a strong argument for training primary care workers in the skills of couple therapy."
Depression is a common mental illness which is estimated to affect up to one in five Britons at some point in their lifetime.
It is estimated to cost the UK about £8bn a year in medication, benefits and lost working days.