As well as activating these opioid receptors, heroin and related drugs have other effects. They cause the release of huge amounts of dopamine from the ventral tegmental area, and they suppress the release of noradrenaline in an area called the locus coeruleus. Noradrenaline is a hormone involved in the body’s fight-or-flight reflex, speeding up our heart rate and breathing to prepare us to tackle a threat (see Chapter 4). It also functions as a neurotransmitter in the brain. Here it helps us feel alert and focuses our attention, but can also produce feelings of anxiety. Suppressing this
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