Alas,
most
drugs that leave the system quickly tend to be the most addictive ones.
Alcohol is only one of them. There is
cocaine, short acting
opiates, amphetamines, all and every one of them is not at all a substitute for
cannabis. It's not only that those substances are much too addictive to be used in a fashion like pot, not one of them mimics the effects of cannabis at all.
Substances that would do so, are the above mentioned synthetic
cannabinoids, which are relatively new substances with not much reliable information and absolutely no long-term-user knowledge. This class of substances also tends to be in the view of legislation and law enforcement.
Long story short:
There is no real substitute for pot, sorry.
Before you decide to try out other substances educate yourself, read on our forums and about the internet,
KNOW what you do! If you don't know, ask!
Stay safe.
TBBW