1. The use of that: a stimulant with regional distribution;Baasher,1980
2. Khat and its use: an historical perspective;Krikorian;J Ethnopharmacology,1984
3. The pharmacology of psychoactive alkaloids from Ephedra and Catha;Kalix;J Ethnophamacology,1991
4. Pharmacological aspects of the chewing of khat leaves;Kalix;Pharmacological Reviews,1985
5. Thompson T. Drug gangs muscle in on million pound new trade. The Observer 2003 11th May 12-13.