 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.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.