IT HAS BEEN hailed in America as a “wonder drug”, able to cure everything from jet lag to cancer. New research suggests that melatonin could also lower high blood pressure — or hypertension — a condition that can lead to heart problems and stroke and which affects an estimated one billion people worldwide.

“This finding might open the door for a new approach to treating hypertension, as anti-hyperintensive drugs have many side-effects,” says Frank Scheer, the neuroscientist at Harvard Medical School who led the research. “No serious side-effects have yet been reported for melatonin, although long-term controlled studies have yet to be performed.”

Melatonin is a hormone produced by the tiny pineal gland in the centre of the brain. It is made only at night — its function is to regulate our internal body clock and so help to maintain regular sleep patterns. It does this by lowering body temperature and making us feel sleepy.

In the 1990s a bestselling American book, The Melatonin Miracle, claimed that a daily dose of the hormone could not only do simple things such as aid sleep or combat jet lag, but also help to prevent ageing, improve your sex life, help to cure asthma and even protect against cancer. Newsweek called the product “one of the hottest pills of the decade”, and although many in the medical establishment called for more detailed research, demand for the product increased dramatically.

Here the reaction was more sceptical, and in 1995 melatonin was classified as a medicine and over-the-counter sales were banned. So although it is widely available in America, in the UK the Department of Health has prosecuted shops and websites for selling melatonin (websites registered outside the UK cannot be prosecuted). Individual doctors are allowed to prescribe it because it is an unlicenced medicine, but they have to “take responsibility” for doing so.

Could Dr Scheer’s research, carried out at the Netherlands Institute for Brain Research (and reported in this month’s American journal Hypertension) change all this? As he explains: “People with high blood pressure often have suppressed night-time melatonin levels. We recently found that they have actual anatomical disturbances of their biological clocks and we wondered if, by restoring the proper function, this could restore proper cardiovascular output and so lower blood pressure.”

The research was carried out on just 16 men (although Dr Scheer says there is no reason why it would be different in women) with untreated high blood pressure. They were given either melatonin supplements or placebos before going to bed — after three weeks, those taking the melatonin found their blood pressure fell appreciably.

Dr Scheer admits that there is a possibility that improved sleep quality helps to reduce blood pressure. However, he points out that his research shows no correlation between the two.

“Melatonin looks deceptively simple,” says Malcolm Lader, Professor of Clinical Psychopharmacology at the Institute of Psychiatry in London. “Because it’s secreted at night and is physiological, you might think it would be safe. But it needs to be treated like any other drug.” Professor Lader is convinced that melatonin is not “devoid of dangers” and that it is right to restrict its availability, particularly because no one yet knows about the effects of long-term usage. “There may be an effect on the reproductive system,” he says. “And melatonin is also known to cause the constriction of blood vessels, which can lead to a heart attack or stroke.”

Dr Scheer also cautions against people immediately taking melatonin to treat hypertension. “Larger studies would be needed prior to recommending this approach to patients with high blood pressure,” he says. “I definitely don’t see melatonin as a ‘wonder drug.’ Such unsupported claims have actually damaged its reputation.”