Drug crimes come in several different varieties, and the connections that exist between drugs and crime can sometimes be very nuanced and complex. Many governments outlaw the use of certain substances, usually in order to protect societies from the behaviors these substances might instigate while simultaneously protecting users from their harmful effects. When people use these chemicals or sell them, they might be prosecuted by the government and sent to jail. There are also crimes that aren't directly related to the use of drugs, but instead have a connection to the way drugs make people behave, and those might also be called drug crimes.
Many governments choose to focus their anti-drug activities on drug crimes related to selling or manufacturing. In theory, this approach is meant to cut off the drug trade at its source. Some people believe this is a more practical approach because drug users usually drastically outnumber suppliers or sellers, which means it generally takes less work and manpower to handle the volume of cases generated.
In some governments, there is also a lot of focus on stopping drug crimes by going after drug users. These countries often try to deter people from using drugs by making the penalties for drug crimes extremely stiff. Often times, people are given a light sentence on their first arrests with increasing penalties for each subsequent arrest. Some people disapprove of aggressive penalties towards drug users because many of them may be addicts, and it may be extremely difficult for them to stop. People who disagree with these aggressive tactics sometimes favor things like rehabilitation instead.
In certain cases, drug use can be connected to crimes that only relate to drugs in an indirect way. For example, an addict might choose to rob someone to get money for the purpose of buying drugs. The primary crime in this example is robbery, but many people would consider it a drug crime as well, because without drugs, it probably wouldn't have happened in the first place. Other examples include infighting amongst illegal drug sellers and crimes dealers commit to avoid being caught by the police.
Some people feel the best way to deal with drug crimes is to legalize more substances, but this approach is fairly controversial. Proponents feel that drug crime enforcement is a serious drain on resources, and they worry that drug laws can create more crime than they stop by generating a black market. Others feel the consequences of legalizing drugs would be far worse than the crimes related to enforcement of drug laws.