I returned earlier this week from Europe and had no problem with either prescriptions or supplements at Customs other than I take many of my supplement in powder form which I keep in my carry on bag so both US and European TSA checked the powder and passed it. Didn't pay any attention at all to the bottles of pills in the same bag.
On a different but related subject, coming back to the US is a breeze if you pay the $100 for a Global Entry pass that lets you bypass the lines by going to a machine that matches your fingerprints or go through the crew line if that doesn't work.
A newer alternative is the free Mobile Passport Control that also speeds things up, but not as much as the above.. [
www.cbp.gov]
Now if they'd only do something about the long wait for checked luggage no matter how fast you get through Immigration.
Gordon