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Monday, 29 July, 2002, 23:13 GMT 00:13 UK
Morphine addiction 'could be blocked'
Brain scan
Morphine kills pain - and causes addiction
Scientists are hopeful they can produce a drug to reduce the addictive effects of morphine, but keeping its painkilling properties.

For years, researchers have been hunting a way to block the brain response which leads to dependence on morphine, and the street drug heroin, which works in a similar way.

All attempts so far have failed, even if the addiction process was diminished, the drugs caused dangerous side-effects.


It's a difficult area of research, but morphine is a very useful drug

Dr Stephen Husband
However, now a research group from the National Institutes of Health (NIH), in the US, believe they have found another route to block addition.

In mice, their method meant that much higher doses of the drug were needed before dependence started to emerge.

However, an addiction researcher from the UK has warned that much more work will be needed before the principle can be turned into a drug for humans.

The morphine molecule causes a number of different effects when it comes into contact with brain cells.

Euphoria

It triggers receptors which produce feelings of euphoria and analgesia - painkilling.

However, these receptors also start a chain of chemical events that appears to lead to dependence.

These are not fully understood.

Doctors have been harnessing the painkilling properties of the drug for generations.

It is particularly useful in tackling post-operative pain, and may be the only drug that helps patients with terminal cancer.

The NIH researchers focused on a previously overlooked brain receptor, called a muscarinic receptor.

Chain reaction

It appears to be involved in the addiction process, but doesn't bind directly to morphine molecules, but to chemicals released by the morphine receptors.

Blocking this part of the chain reaction might lessen the addictive effects, they reasoned.

They bred mice genetically modified to lack these muscarinic receptors, then gave them morphine.

The pain relieving effects of the drug remained, but the mice had far less severe symptoms of morphine withdrawal when taken off the drug.

The scientists think the new receptor might have potential as a target for a blocking drug in humans.

Although its role in other brain functions is poorly understood as yet, it can be found only in very limited areas of the brain, so the chances of serious mental side effects are perhaps lower.

Fruitless effort

Dr Stephen Husbands, a medicinal chemistry research fellow at the University of Bath, has been involved in his own research project into the chemistry of addiction, funded by the US National Institute on Drug Abuse (NIDA).

He told BBC News Online that much exciting research had been directed at ways to block morphine addiction, but clinically useful drug remained elusive.

"It can take a very long time to get approval for drugs such as these and a lot of them fall by the wayside.

"It's a difficult area of research, but morphine is a very useful drug."

The research was published in the Proceedings of the National Academy of Sciences.

See also:

23 Dec 99 | Health
20 Jul 99 | Health
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