THC is not like lean. Although they share their roots in hip-hop culture, they are entirely different beverages.
Lean is prescription codeine-promethazine cough syrup mixed with another drink like soda or alcohol. It is highly addictive. It is also called purple drank, dirty sprite, or sizzurp.
THC syrup is completely free of opiates and does not carry the same level of danger or intoxication.