DB provides a lot of info and relevant links on their members page. It's worth your time to read up on the laws, as there are always rumors floating about. The bottom line is that yes, it's illegal to import drugs to the US. Other countries have their own laws. These overseas OPs stay in business because they offer what people want and usually have a much better price than brand-name, with very similar results.

Here's a link to get you started:
https://drugbuyers.com/members/uscustoms/

Take Care,
Toky