One of the key elements of drug crime law in the criminal justice system is the scheduling system. "Schedules" are classifications that the Drug Enforcement Agency and the government use to determine which drugs and substances can be abused and have a high chance to cause addiction. The higher up the scheduling system a drug or substance is, the more punishing the consequences are for possessing, using or distributing that drug or substance.
You probably heard schedules mentioned earlier this year, when the DEA was considering reclassifying marijuana as a Schedule 1 substance (the highest in the system). Marijuana was ultimately left with its Schedule 1 designation, meaning people who possess and distribute the substance will be harshly punished and it also limits the ability of scientists to study marijuana for its medical benefits.