They don’t care if you bring them back. They put them in a disposal system and won’t document who you are.
The only time prescription monitoring comes into play is if you’re filling more than a normal amount. Some states have limits on pain pills or morphine equivalents. Unless you’re popping 10 a day and begging docs for refills, nobody gives a shit.
Are you afraid of becoming addicted? Or just that they won’t give you pills when you need them?