system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What is the difference between generic and name brand drugs and how are generic drugs so much cheaper?
gpt
So drug company A spends 7 years and $1,000,000,000 dollars to develop Gropax. They apply for a patent, and receive a 20 year patent. For 20 years, they are the only people allowed to manufacture Gropax. They sell it at a price high enough to make back all of the money that they spent developing it.

After the 20 years is up, any one is free to make the drug. They can use the formula and sell it under any name except Gropax. So company 2 comes in and begins making the drug. Because manufacturing pharmaceuticals is very cheap, they can sell the generic drugs very cheaply.