Answer:
Although all medicines are drugs, some drugs can't be used in medicines because it can kill you or pose a health risk. Medicines are chemicals or compounds used to cure, halt, or prevent disease; ease symptoms; or help in the diagnosis of illnesses. In this case, some drugs do the exact opposite: instead of curing it can kill or make your health condition worse.
Example: Cannabis/marijuana is a psychoactive drug. It can give several health risks, and it can make your mental health worse.