Drug abuse is when you use legal or illegal substances in ways you shouldn't. For example, you may take more than the regualr dose of pills or use someone else's prescription. Many drug abuser use drugs just to ease their stress, to feel good about themselves or just to avoid reality. Abuse of drugs inculde herion, methamphetamine, anabolic steroids,marijuana, opioids and several other variations.
Addiction is a disease that affects your brain and behvaior. Being addicted to drugs means that you can't resist the urge to use them even when it puts your health in danger. Drug addiction isn't about just herion, cocaine, or other illegal drugs, but you can also be addicted to alcohol, nicotine, opioid painkillers, and other legal substances.
The link below best decribe the reasoning behind substance abuse and addiction: