Drug

1. A substance used to treat an illness, relieve a system, or modify a chemical process in the body for a specific purpose. Drugs have saved many lives.
2. A substance, sometimes addictive, which affects the central nervous system. The drug cocaine can end your life.
3. A substance, especially one that is illegal, ingested for recreational use. Marijuana is a mind altering drug.
4. To administer intoxicating drugs to, generally without the recipient's knowledge or consent. The man drugged her so he could take advantage of her.