A medicine to combat insomnia similar to jet-lag supplements favoured by travellers has been launched in the UK.
Circadin contains melatonin, a natural hormone released in the brain that helps to regulate sleep.
Melatonin supplements are widely available in the US but cannot be found over the counter in the UK due to fears about side-affects. Circadin is the first melatonin product in Britain to be licensed as a prescription drug.
But it will only be available to adults aged 55 and over who suffer from "primary insomnia" - difficulty sleeping that is not due to any medical condition or taking substances such as drugs or alcohol.
Melatonin helps to set the body clock, or circadian rhythm, that decides sleeping and waking times and affects many biological processes.
Sleep problems often arise as a result of falling levels of melatonin, or the hormone being released at the wrong time.
Supplements containing natural or synthetic melatonin are taken by many long-distance travellers to combat jet lag, which is caused by disruption of the sleep cycle.
Circadin is synthetic melatonin that comes in 2mg tablets. It is supposed to be taken for no more than three weeks to get the body back into a regular sleep pattern.