In a previous column I highlighted the unhappy association between antidepressant use and heightened risk of suicidal behaviour in children and adolescents. Evidence has just come to light which suggests that this link may not be confined to the young. Research published recently in the British Medical Journal shows that taking selective serotonin re-uptake inhibitor (SSRI) type antidepressants (including fluoxetine [Prozac] and paroxetine [Seroxat]) may double the risk of suicide attempt. The acting editor of the BMJ questioned how many people who have turned to 'happy pills' would not have done so if they had been fully aware of the risks.

Yet just a week prior to the publication of this study there was cheerier news in the BMJ: German researchers have found that the herb St John's wort (hypericum perforatum) is at least as effective as the drug paroxetine in relieving moderate to severe depression. Not only that, but its capacity to induce side-effects was substantially lower than that of the conventional drug.

This is the latest in a mass of evidence which shows St John's wort can put a smile on the faces of those seeking a natural remedy for depression. Several studies have found it to be more effective than placebo (inactive medication) and about as useful as conventional antidepressants. What is noteworthy about the BMJ study is that it suggests that the herb may benefit those with severe depression, too.

Scientists believe that St John's wort's antidepressant action is attributable to two compounds, hypericin and hyperforin. Extracts of the herb potentiate the feel-good brain chemical serotonin in a way reminiscent of the SSRI drugs. It also appears to boost the effect of chemicals that are believed to have an antidepressant action, including noradrenaline and dopamine.

Although generally safe, St John's wort can increase the metabolism, reducing the effectiveness of drugs such as indinavir, cyclosporin, digoxin, warfarin, and the pill. Those who take these drugs should use it under medical supervision. The recommended dose is 300mg of extract, taken three times a day. Benefits are apparent within two to four weeks. Those on conventional antidepressant medication should not reduce this without consulting their doctor. That said, considerable evidence suggests that for those seeking a natural alternative to antidepressants, St John's wort is certainly worth bearing in mind.

Dear John

I had my first child seven months ago. I am eating healthily (mostly natural, unprocessed foods, limited sugar and starchy carbohydrates). I walk for at least half an hour a day and go to the gym once or twice a week. Frustratingly, I am still 2.5 stone heavier than I was before. Do you have any advice?
LH

In my experience, a common and frequently overlooked cause of problems with weight loss after pregnancy is impaired function of the thyroid gland. The activity of the thyroid has a big hand in determining the speed of our body's metabolism, and therefore weight. Low thyroid function can be 'triggered' by pregnancy and cause persistent weight issues. It may be associated with symptoms including sensitivity to cold, cold hands and feet, dry skin, dry hair, fatigue and constipation. If you have some of these symptoms, then I would suggest you have a blood test for thyroid function. However, in my experience, blood tests can fail to pick up genuine cases of low thyroid. For information on the diagnosis and treatment of low-thyroid function, go to www.thyroiduk.org.

Nutrition news

I recently wrote about the potential health benefits to be had from drinking green tea, including relative protection from several forms of cancer including those of the breast and prostate. Compounds in green tea known as polyphenols have what is known as 'antioxidant' activity, which means that they have the ability to quell the 'free radical' molecules which are implicated in the cancer-causing process.

Recently, scientists from the University of California in Los Angeles examined the effect an extract of green tea had on human bladder cancer cells. The green tea extract was found to have the ability to impair the movement of cancerous cells, reducing their propensity to invade healthy cells and tissues. By impairing the spread of cancerous cells, green tea might improve the prognosis of cancer and make it easier to treat successfully.

This study, which was published in the medical journal Clinical Cancer Research, provides further insight into how the drinking of green tea may help to combat cancer in the long term.

· Natural Health for Kids by Dr John Briffa is published by Observer books