Lipitor, Prozac, Viagra. These names are marketing, not chemistry. A brand-name drug is a product sold under a proprietary name by the company that developed it, usually protected by patents that block competitors for years. The chemical name might be atorvastatin, but the brand is what patients recognize and what the company promotes.

Developing a new drug costs roughly a billion dollars and takes a decade or more. The patent system grants exclusivity as a reward, allowing the company to set prices high enough to recoup that investment. When the patent expires, generics enter the market at a fraction of the price. Atorvastatin, for example, went from a blockbuster brand to a commodity generic in a few years, with prices dropping by more than 90 percent.

What distinguishes a brand-name drug:

• Proprietary name. Chosen by the company and protected by trademark.
• Patent protection. Usually 20 years from filing, though the clock starts before approval.
• Pricing. Set by the manufacturer, often high during exclusivity.
• Marketing. Direct-to-consumer advertising in some countries, restricted in others.

Generic versions must contain the same active ingredient, at the same strength, and be bioequivalent. They may differ in color, shape, and excipients.