A study by the University of Geneva is shedding some light on why the opiate fentanyl is so addictive.
The findings may help on making a less harmful painkiller and could lead to better treatment for those already addicted, say the researchers.
The drug is responsible for thousands of deaths in the United States – and its effect is starting to be felt here.
Fentanyl is 50 times more powerful than heroin and triggers feelings of euphoria and then a mood crash.
But the new findings show it affects two distinctive areas of the brain. The team says this massively changes the understanding of how the drug hooks its users.
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