An extract from the herb St John's Wort is just as effective as a drug commonly used to treat depression, according to medical researchers.

A German study compared the effect of hypericum extract and the drug imipramine on 263 moderately depressed patients.

The researchers, led by Professor Michael Philipp from Landshut district hospital, found that hypericum was as effective as the drug and had fewer side effects.

Quality of life, both physical and mental, was significantly improved after the patients had been taking hypericum for eight weeks.

Alternative treatment

The herbal extract is already widely used to treat mild depression in Germany.

However the dosages used in the trial, 350mg three times a day, were higher than those normally recommended - and the prescription antidepressant compared against it is an old drug with more side effects than the latest varieties.

Victor Perfitt, of the British Herbal Medicines Association, stressed that it should never be used as a treatment for clinical depression, only the milder forms of the condition.

"We would never encourage irresponsible marketing of St John's Wort," he told the BBC.

Writing in the British Medical Journal, the researchers concluded: "Since many depressed patients receive either no treatment or inadequate treatment after an initial depressive episode and are at increased risk of recurrence of such episodes, hypericum extract may ... be considered as an alternative first choice treatment in most cases of mild to moderate depression without psychotic symptoms."

St John's Wort has been used for many years in folk medicine to treat disorders such as burns, wounds and depression.

More recently it has gained popularity as a natural anti-depressant.

Total sales in Europe were around $6bn in 1998.

The herb is available as dried leaves and flowers, a concentrated liquid or tincture extract, in capsules and ointment and prepared tea.

Side-effect warning

It is thought to work in a similar way to anti-depressants known as serotonin-reuptake inhibitors which relieve depression by increasing the availability of serotonin, a neurotransmitter associated with mood.

But Dr Edzard Ernst, of the Department of Complementary Medicine at the University of Exeter also warned it could reduce the amount and the effects of other medicines.

In a commentary in The Lancet medical journal on Friday, he cited several cases when St John's Wort reduced the effects of anti-blood clotting drugs and the contraceptive pill in women by as much as 40%.

"If you take St John's Wort it will induce a family of enzymes in the liver which is responsible for breaking down a lot of prescribed drugs," he said.