Does the fifth precept ban smoking? The fifth precept started off as a ban on the drinking of alcohol. It has since been expanded to ban the use of intoxicants. Is tobacco also forbidden under the fifth precept?
I always approached the precepts as very important guidelines rather than rigid rules for banning one's actions. 

Certainly, while on the eightfold path, if one intakes a substance that even subtlety  clouds the mind  then that substance would lead to one's suffering and the suffering of those around one. The more one understands this and the more one sees things as they are, the more one will follow the presepts naturally like a river follows the best way down the side of a  mountain.-Metta