The High Court has ruled a woman in a persistent vegetative state given an experimental treatment against her family's wishes can be allowed to die.
Zolpidem works on nerve cells in the brain
It had been ruled, despite her family's view, that she should be given a sleeping pill which could potentially have woken her up.
However, the 53-year-old, who has not been named, failed to respond to the drug, zolpidem.
Her doctors will now be allowed to withdraw life-sustaining care.
Early reserach had shown that zolpidem can bring people out of a vegetative state.
But the woman's family did not want her to receive the drug, preferring to let her die, as she may be left seriously disabled.
They were also concerned she might awake temporarily and realise the condition that she is in.
Sir Mark Potter, head of the High Court's family division, ruled against their wishes earlier this month.
He gave the go-ahead for a three-day trial course of zolpidem after hearing that it might offer her a "glimmer of hope" of recovery.
The drug proposal had been put forward by Laurence Oates, the outgoing Official Solicitor.
Zolpidem is normally used to help insomnia but has been cited in a number of cases where it has caused patients in a persistent vegetative state (PVS) to wake up.
In these cases, an improvement was seen within 20 minutes of taking the drug and wore off after four hours, when the patients were restored to their vegetative state.
But at a hearing in London on Wednesday, Sir Mark said the drug had failed to boost her level of awareness.
He said: "The drug produced no increased responsiveness and instead it appeared to make her fall asleep, that is to say it had its normal intended effect, it being a form of sleeping pill marketed as effective in dealing with cases of insomnia."
The woman was diagnosed as PVS after she suffered a brain haemorrhage while on holiday in August 2003.
Professor Keith Andrews, of the Royal Hospital for Neuro-disability, gave evidence at the original hearing.
He supported the way it was handled by the courts.
He said: "Although the outcome is as we had anticipated, we felt it was important to support the view that everything should be done that could be done before any decision was made to withdraw nutrition and hydration."
Members of the woman's family - said to be loving and close knit - were present in court, including her husband and one of her daughters, but they did not wish to comment.
It is not the first time a PVS patient has caused ethical problems.
In 1993, the Law Lords ruled that Hillsborough stadium disaster victim Tony Bland could have his feeding tube removed.
The 22-year-old was crushed and his brain starved of oxygen during the FA Cup semi-final disaster in April 1989, when 96 people died.
For nearly four years he was in a persistent vegetative state.