Conversion to either Christianity or Islam often depended upon where you were along the Vodka-Hashish axis. When the Medieval Byzantines expanded into Kiev, the final decision by the Chief to convert to Orthodoxy was made when he learned that Christians could drink alcohol.
When the Seljuk Turks swept down from the Asian steppes and made contact with the Moslem's in Persia, they converted to Islam when they learned that the use of hallucinogenics was permitted.