I travel between Canada and US about 4-5 times per year and never had any issues except as noted below. The only issues I have had flying into or out of the USA involved bottles in carry-on bags. I put some bottled waters in my carry on bag and was hassled by security at the Westchester, NY airport while waiting for a flight to the Bahamas. Initially they were going to seize the water bottles, but after they saw all the prescription meds in my bag (cipro, flagyl, pentasa, imodium, levsin, etc.) they bought my plea that I have medical issues that require constant hydration. They gave me a pass on the water bottles, although I later learned that Jet Blue (which I was flying at that time) does give complimentary small bottled waters, so it wasn't necessary to pack them.
More recently on a flight from Tampa, Florida to Hartford, CT, I unwittingly packed a metal canister of Coppertone spray suntan lotion, and this was seized. You can't put stuff like that in a carry on bag. Any metal canister over a certain size will get seized. It kind of sucked because it was a $10 bottle that I had only used once, but I learned my lesson not to do it again.
About 5 years ago driving back from the Montreal Jazz Festival, US customs authorities at the Vermont border seized $300 worth of tea I had purchased in Montreal's Chinatown #1. The reason for the seizure was that it was packed in unlabelled zip lock bags and there was no way for them to know what the contents were. They were an assortment of black teas from southeastern China from what the tea merchant told me- I had purchased them before- they were lychee and some other types of flavored black teas. I had made numerous purchases before in smaller quantities, and never had a problem, but the tea was seized despite my protest. I wasn't fined, because I had declared the tea. Anyway if you bring in something in a loose pack, unlabelled and they cannot instantly identify the contents, expect seizure. There is a US federal regulation from what customs authorities told me, requiring packaging and identification of the packaged product. It might be different with pills but keep the original bottles so you can identify them if needed.