Scientists say they now know more about what happens in the brains of former drug addicts when they crave cocaine. Tests on rats by US National Institute on Drug Abuse researchers found a way of blocking craving messages in their brains and preventing a relapse. Nature Neuroscience says the findings suggest the danger time is not straight after addicts stop taking the drug, but after they go long periods without it. The study found a protein in the brain plays a part in triggering cravings.