Prescribing antidepressants on top of mood stabilizers for people with bipolar disorder provides no extra benefit, a U.S. study has found.

Also called manic depression, bipolar disorder is a condition in which people have severe mood swings, from periods of excess energy and restlessness to serious depression.

Mood stabilizers such as lithium can reduce mania but depression is more common than mania in bipolar disorder and the depression episodes tend to last longer.

Antidepressants are often used with a mood stabilizer, although the U.S. Food and Drug Administration has not approved the drugs as a treatment for the disorder.

In Thursday's New England Journal of Medicine, Dr. Gary Sachs of Massachusetts General Hospital in Boston and colleagues compared 366 people with bipolar disorder who were randomly assigned to receive one of two antidepressants, Wellbutrin or Paxil, or a placebo for 26 weeks, in addition to appropriate doses of mood stabilizers.

Neither the patients nor the doctors knew who was in each group.

Of the 179 subjects who received an antidepressant and mood stabilizer, about 24 per cent were able to go eight weeks with no more than two depressive or manic symptoms.

In comparison, 27 per cent of those in the placebo group reached the same level, a difference that is not statistically significant, the researchers said.

Some antidepressants are thought to increase the risk of a switch to a manic episode, but the team found no evidence of that for Wellbutrin or Paxil. About 10 per cent of each group experienced emerging symptoms of mania.

Study included people with additional disorders

Study participants also received psychological and social therapy.

Since the study was designed to mimic real-world conditions, it included patients with additional disorders, such as anxiety, substance abuse or psychosis.

"If you are on mood stabilizer treatment, which is the best first-line treatment for most people with bipolar disorder, adding an antidepressant usually does not help you out of your depression," said Dr. Lauren Marangell, of the department of psychiatry at Baylor College of Medicine in Houston, one of the lead investigators.

"As first-line treatment for depression in bipolar disorder, we do not recommend antidepressants," Marangell said. Antidepressants may help in individual cases, particularly in those with other problems, and the decision is up to each physician, she added.

In general, careful management of mood stabilizer medications is a reasonable alternative to adding antidepressants for treating bipolar disorder, Sachs said. Longer term studies are needed to fully assess the benefits and risks of antidepressant therapy for bipolar disorder, the researchers concluded.

The results suggest that antidepressants are safe but not more effective than a placebo in people with bipolar disorder, agreed Thomas Insel, director of the National Institute of Mental Health, which funded the study.