I think you're overthinking it ... (a lot) !
As a Canadian, we also travel with a similar pharmacy and like the UK, brand names may be different!
From what I can see, the only drug not available in Canada or the States is Stugeron - I mean, if a customs officer was interested enough to open up your bag, find it and look it up, he would (probably) have the right to confiscate it but that's a real stretch! Original packaging or blister packs are more than enough!
Problems could occur with people (like me!) who will just take the trip's worth of Vitamin D's, Ca and other supplements and put them into unlabelled medicine bottles - now that looks suspicious! In all my hundreds of trips to the States, they've never been concerned. Their main "everyday" contraband that they're very concerned about remains food products ....