According to the Mayo Clinic, substance use disorder - also called addiction, is a disease
- A disease that affects a person's brain and behavior and leads to an inability to control the use of a legal or illegal drug or medication. Substances such as alcohol, marijuana and nicotine also are considered drugs. When you're addicted, you may continue using these substances despite the harm it causes.
Addiction can start with experimental use of a recreational drug or alcohol in social situations. For others, particularly with opioids, addiction begins with exposure to prescribed medications, or receiving medications from a friend or relative who has been prescribed the medication.
Learn more about substance use disorder here: