A drug is a substance or chemical that affects the way our bodies and minds work. Some are artificial and others come from plants, minerals, and animals.
A drug is a chemical used in the diagnosis, cure, mitigation, treatment, or prevention of disease to bring about an alteration in one's mental or emotional state. (Chemistry of Drugs by Newton)
Aspirin (from willow bark; used for pain) Caffeine (from coffee, tea, cocoa; used as a stimulant) Cannabis (from cannabis sativa or marijuana plant; recreational drug having some benefits in medicine) Digitalis (from foxglove; used for the heart) Taxol (from yew tree; used in the treatment of cancer) Tobacco (from nicotiana tabacum; recreational drug used mainly by smokers)
Designer Drug
A synthetic chemical compound developed for the treatment of a variety of diseases and disorders--aka club drug, rave drug, controlled substance analog.
Orphan Drug
Orphan drugs are used to treat a "rare" or extremely rare disease. A disease only found in just a few people. Since there is no need to mass produce the drug, pharmaceutical companies are unlikely to recover the costs for research and development.