Substance abuse is an inability to control the use of a legal or illegal drug or medication. Substances such as alcohol, marijuana, particularly with opioids, drug addiction can begin with exposure to prescribed medications or receiving medications from a friend or relative who has been prescribed the medication. When you're addicted, you may continue using the drug despite the harm it causes.
Drug addiction symptoms:
Having intense urges for the drug that block out other thoughts
Needing more of the drug to get the same effect
Spending money on the drug, even though you can't afford it
Spending all your time getting the drug, using the drug, or recovering from using the drug.