A generic drug is a clone of the brand-name drug with the same dose, safety, strength, quality, how it’s taken, performance, and intended use. Before generics were available on the open market, the generic company must prove it has the same active ingredients as the brand- name and works the same way inside the body in the same timeframe.
The only difference between generics and their brand-name counterparts is the generics are less costly and may look slightly different (e.g. different shape or color), as trademark laws stop a generic from looking exactly like the brand-name drug.
Generics are less costly because generic manufacturers don’t have to invest large amounts of capital to create a drug. When the brand-name patent expires, generic companies can manufacture a clone of the brand-name drug and sell it at substantial discounts.