A controversial abortion pill may have a use as an anti-depressant, say researchers in the United States and France.

The pill, known as RU486 or mifepristone, is available in both countries.

It has met with opposition from anti-abortion campaigners, particularly in America where it was authorised only in September 2000.

A study published in a US journal, Biological Psychiatry, suggests it may be a potential therapy for psychotic depression, a severe form of the illness.

Patients with psychotic depression suffer from hallucinations and delusions as well as the typical symptoms of depression, such as feeling hopeless and low.

The treatment is different from other major depressive illnesses and the risk of suicide is greater.

The small-scale study on a group of 30 volunteers was carried out by the inventor of RU486, Etienne-Emile Baulieu, and a team from Stanford University in California.

Use of the pill dampens surges of the stress hormone cortisol, implicated in this form of depression, they say.

Dr Baulieu told the news agency Agence France Presse that RU486 "can save lives".

"A week's treatment with RU486 helps the patient to overcome the danger, and return to normal medication," he said.

Stress link

Dr Anthony Cleare of the Institute of Psychiatry in London described the approach as "experimental".

He said one theory is that stress leads to depression via the body stress hormone cortisol.

It could contribute to some of the features of depression such as low mood and changes in sleep patterns.

Researchers are working on ways to block the effects of cortisol either by stopping its production or blocking its action on the brain.

"The evidence seems to be coming together that cortisol might be one of the factors in depression that links stress to the physical symptoms of depression," he told BBC News Online.

"So intervening in that pathway may have promise for the future but more studies are needed."