The main drug used to resuscitate cardiac arrest victims has needlessly left thousands of people with brain damage, according to a major new trial.

Adrenaline, which paramedics inject when CPR (Cardiopulmonary resuscitation) and electric shocks are failing to work, barely improves the chances of living but nearly doubles serious neurological harm among those who do survive.

Scientists believe it may damage the function of blood vessels in the brain, leaving patients in a vegetative state.

Either that or adrenaline causes damage because the heart can survive without oxygen for longer than the brain, meaning that although it can be restarted the brain is likely to be permanently impaired.

The drug is given to around eight in ten of the 30,000 people who suffer a cardiac arrest - when the heart stops beating - outside hospital every year in the UK, of whom only 10 per cent survive.

The findings of the study by the University of Warwick means health leaders may ban ambulance crews from using it.

The authors said the results further highlighted the importance of CPR and defibrillation skills among the public.

Published in the New England Journal of Medicine, the study involved 8,000 patients across five ambulance areas in England between 2014 and 2017.