"Although rTMS treatment has not yet lived up to early hopes that it might replace more invasive therapies, this study suggests that the treatment may be effective in at least some treatment-resistant patients," said Dr Thomas R. Insel, director of the National Institute of Mental Health (NIMH).

rTMS treatment accounted for remissions in 14 per cent of antidepressant-resistant patients -- compared to about 5 per cent for the control group who were given a simulated treatment as a placebo.

"This study should help settle the debate about whether rTMS works for depression," said team leader Dr Mark George of the Medical University of South Carolina.

"We can now follow up clues suggesting ways to improve its effectiveness, and hopefully further develop a potential new class of stimulation treatments for other brain disorders."

The study indicated some patients might require as many as 5-6 weeks of daily rTMS treatment.

Most patients who went into remission required 3-5 weeks of treatment.

"For treatment resistant-patients, we found that rTMS is at least as good as current medications or anything else we have available, except ECT," said Dr George.

"Our current antidepressants do not work for many people."