<P> Receptors for serotonin show a high affinity for cathinone, suggesting this chemical is responsible for feelings of euphoria associated with chewing khat . In mice, cathinone produces the same types of nervous pacing or repetitive scratching behaviours associated with amphetamines . The effects of cathinone peak after 15 to 30 minutes, with nearly 98% of the substance metabolised into norephedrine by the liver . </P> <P> Cathine is somewhat less understood, being believed to act upon the adrenergic receptors causing the release of epinephrine and norepinephrine . It has a half - life of about three hours in humans . The medication bromocriptine can reduce cravings and withdrawal symptoms within 24 hours . </P> <P> An estimated 5 to 10 million people globally use khat on a daily basis . It is grown principally by communities in the Horn of Africa and the Arabian peninsula, where khat - chewing has a long history as a social custom dating back thousands of years . </P> <P> The traditional form of khat chewing in Yemen involves only male users; khat chewing by females is less formal and less frequent . Researchers estimate about 70--80% of Yemenis between 16 and 50 years old chew khat, at least on occasion . Approximately 60 - 90% of male and 35% of female Yemenis chew khat daily . Prior to Yemeni unification in 1990, khat chewing was largely confined to the north - west mountains of the country, where khat grows . Yemenis spend an estimated 14.6 million man - hours per day chewing khat . Researchers have also estimated that families spend about 17% of their income on khat . </P>

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