Is it illegal to sell expired over-the-counter medication in colorado or the USA?

The state authorities will fine me for having expired product anywhere
in my practice unless it is obviously in the process of being
discarded. The state licensing board will reprimand and fine me if I
use expired product; they have the right to impose other penalties as
well, including suspension. Both of these situations even apply to
autoclaved (sterilised) instruments.

Any store that knowingly or otherwise has expired medicine on display
should be avoided and (if a chain) notice sent to the headquarters
office.

Mind you, medicine doesn't "turn off" on the expiration date. A few
days is okay, a few weeks less so, and a few months is inexcusable.

Coincidentally, I found three cottage cheese containers that were a
week expired in my local grocery store yesterday. Shameful.