Using alcohol and cocaine at the same time seems to produce a third substance that may yield a greater high but also may raise the risk of death by overdose, scientists reported last week at the annual meeting of the Society for Neuroscience.

The research, along with a preliminary finding that drinking boosts the risk of a fatal cocaine overdose about 20-fold in people with severe coronary heart disease, may help explain the puzzling overdose deaths in people with surprisingly little of the drug in their bloodstream.

New studies show that this third substance, manufactured in the liver from cocaine and alcohol, can mimic some actions of cocaine in the brain. Alcohol is often used in combination with cocaine, according to the National Institute on Drug Abuse.

The substance is a close chemical cousin of cocaine called cocaethylene. Further studies of it may help development of leads for medications to treat addiction by blocking cocaine's effects, said study co-author Deborah Mash, a neuropharmacologist at the University of Miami School of Medicine.

Scientists found that cocaethylene affects a brain cell communication system thought to produce the euphoria that leads to addiction, she said.

The new study shows that cocaethylene may boost cocaine's effect, keeping the pleasure signals in the brain turned on, Mash said. In addition, she said, it appears less able than cocaine to moderate euphoria and may interfere with the brain's control of the heart's pumping rhythm. If the heart is already affected by disease, the result could be sudden death, she suggested.

Michael Kuhar, a NIDA neuroscientist who did not participate in the studies, said the suggested roles for cocaethylene are plausible. It is "a new entity we don't know much about," he said.