St John's Wort 'can lead to pregnancy'

New evidence has emerged that a herbal remedy to treat mild depression may counter the effects of the contraceptive pill.

There have been reports of at least two women becoming pregnant while on the Pill, with the most likely cause of failure thought to be the effects of St John's Wort. The supplement, dubbed "nature's Prozac", is made from the dried flowers of the yellow hedgerow plant and is taken regularly by an estimated two million people in this country.

It is known to stop certain prescription drugs from working properly and in the UK packets now carry warnings although the herb, as an unlicensed medicine, is available without prescription in health shops and pharmacies.

The Swedish pharmaceutical regulator, the Medical Products Agency (MPA), has revealed that taking St John's Wort has resulted in two women, aged 28 and 31, becoming pregnant even though they were on the Pill.

The MPA said that other cases of unwanted pregnancies had emerged in the past, including a number in the UK, prompting the British government to issue advice two years ago to women on the Pill not to use the herb. Per Claeson, from the MPA, said: "We have heard of several case reports of pregnancies occurring in Sweden and the UK, and drug interactions also in Switzerland and Germany. We issued advice on this in 1999 but we are making it clearer now because we are more sure.

"The evidence has come from clinical interaction studies and also biochemical research. What is really new is that we have found some products have less of an effect than others, and these have been allowed a milder form of labelling."

Another official from the authority added: "Considering the number of women this is affecting, this is important information."

In light of the most recent scientific evidence, Sweden has now made it compulsory for all St John's Wort products except tea to carry a warning label about drug interactions.

The European market for St John's Wort is said to be worth around £3.75 billion a year. The herb has been used as a medicine since AD 100, and according to legend, was discovered by St John the Baptist.

There is strong evidence that the herb can lift the symptoms of mild to moderate depression and it is also known to have fewer side effects than prescription drugs.

However, research shows that St John's Wort can reduce the effectiveness of HIV medicines, blood-thickening drugs, and cyclosporine, a drug used to prevent rejection of organ transplants.

A spokesman for the UK equivalent of the Swedish MPA, the Medicines Control Agency, said that since March 2000 there has been a voluntary agreement between manufacturers to provide such information with products. At that time the MCA issued advice to health professionals listing the kind of drugs St John's Wort may affect, including oral contraceptives.

An MCA spokesman said: "The subject of St John's Wort interacting with other medication first arose in 2000 and the MCA issued advice to the public and health professionals. Our advice has not changed since then."