Cocaine addicts may get spikes in a brain chemical associated with a high at the mere anticipation of a "hit", suggests a new study in rats.

US researchers found that dopamine, a neurotransmitter associated with pleasure, surged before rats pressed a lever to release a dose of cocaine and even while they were waiting for the hard drug to be delivered.

Dopamine is known to peak during addictive behaviours like drug taking, eating and sex, but this is the first study to demonstrate an increase before the actual event. The finding could help understand why recovering drug addicts relapse, say the researchers.

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