Painkiller that comes with a health warning

If Demerol, the powerful opiate painkiller, turns out to be responsible for Michael Jackson's death, it may be that he had an unexpected reaction to the drug, rather than receiving an overdose, according to a leading British expert on drug abuse. Jackson was known to have been dependent on Demerol, the US brand name for pethidine, for years. Pethidine is a powerful opioid painkiller similar to morphine and users report that, as well as eliminating pain, the drug produces a warm, comforting, "cotton wool" effect. In the 1970s and 1980s, it was used widely in Britain to alleviate the pain of childbirth, but is prescribed less today.

Professor John Strang, the director of the National Addiction Centre at the Maudsley Hospital, London, said occasionally addicts of opioid drugs such as heroin died of "overdoses", despite injecting the same controlled dosage that they usually used.

"It suggests one cause of overdoses may be not that people get the dose wrong, but something else – perhaps to do with the flow of the blood. If the flow is slowed, a plug of opiate might not get diluted properly and hit the brain in a concentrated form [having the same effect as an overdose]."

One question over the Demerol theory is why, if the drug was the cause of Jackson's collapse, his doctor did not administer an antidote. Naloxone is an established antidote to opiate overdose and if given soon enough, saves lives. It would have been a simple matter to administer an injection of naloxone, had one been available.

The autopsy should provide a definitive answer. But that could take weeks because sophisticated toxicology tests will be required to determine which, if any, drugs were in his system.