What kind of substances are called drugs​

It depends on the context (as in which type of drug you are referring to).

Explanation:

When it comes to common drugs that a pharmacy would have (also known as medicine), those are chemical substances used to diagnose, treat, prevent, and/or cure a disease or sickness.

However, if you're referring to drugs like cocaine and meth, those are psychoactive drugs. They typically affect the nervous system's functions and changes perception (our ability to recognize things), mood, and consciousness. Some psychoactive drugs are used to treat medical conditions, but have a few restrictions to ensure the patient/recipient dos not get addicted.

the density would be a smaller number.