A substance used as a medication or in the preparation of medication.
The doctor prescribed a new drug to help manage her symptoms.
A substance that has a physiological effect when ingested or otherwise introduced into the body, especially one that is illegal or used recreationally.
He was arrested for possession of illegal drugs.
Something that produces a strong, often addictive attraction or pleasure when experienced; a figurative source of dependency.
For many people, social media has become a drug they cannot live without.