I thought I had a decent handle on patent law, but maybe I'm missing something here. Yes, the patent won't be valid for Canada, but you can't import a product into the US which would infringe on a US patent. So, though there may be a small amount that would slip through the cracks, it isn't as if anyone in the US can now manufacture Semaglutide and distribute it. Canada is such a small market, that many companies don…
Canadian pharmacies can legally sell it and Americans (and all other foreigners for that matter) traveling there can legally buy it.
Unlike the criminal law, Novo nordisk would have to go after every single person individually and make the case that they are infringing the American patent. This is all without the help of the police or customs, as a private civil matter.
Obviously this would be uneconomic for Novo Nordisk. You can't search anyone as you don't have any warrants, as it's not a crime and then even if you could, you need to prove that the drugs they have on them were purchased in Canada.
Foreigners who currently pay a huge amount of money would only have to make one trip to Canada in however long period it takes for the drugs to expire. I know I would certainly make a day trip if I was using this drug.
Intellectual property law firms offer services to renew and watch registrations like this worldwide and it would have been very simple to have a contract with one of them.