First, worth noting that this is very much TBD. There are grave 1st Amendment concerns with the government's efforts there and it is very much an open question for now whether the effort will actually hold up in court. That said:

>what’s stopping Uncle Sam commandeering Novo to either sell off its Ozempic ownership as a subsidiary to force a lower general sales price, or forcing to nullify its patents? I’m speaking legally rather than economically.

So as a practical matter, and as with TikTok, Novo Nordisk is not a domestic company it's a foreign one. But unlike TikTok where China is a geopolitical opponent, Novo is Danish and thus part of a close ally. Second the people pushing the TikTok thing are fine with TikTok going away entirely in the US, that's the stick. The US has zero power jurisdiction over China just as the reverse is true, but can police its own market and thus say "comply or lose access to our market". Same as how the EU is pushing stuff like the DMA. Since the US market is valuable that's a sizable stick, but TikTok very likely even if they lose will tell the USG to pound sand and just leave, but Congress/WH wouldn't mind that.

But here the whole point is that people desperately want this product. So if Novo said "no, and we're ceasing all sales in the US" they'd take a major financial hit sure, but there'd also be massive blow back in domestic and international politics. It would definitely be questioned on various US/EU trade agreements which would have messy legal implications, and invite tit-for-tat. Nationalizing foreign IP would implicate a bunch of treaties and US itself pushed hard and benefits from.

But putting all that aside and pretending it was all domestic (or going specifically after domestic components), there is still the Takings Clause of the 5th Amendment. The government could legally seize it using eminent ___domain powers, though it'd no doubt face as good a legal fight as the highest paid law firms could put on. But I don't think there's any doubt this would be a clear case of public use and courts have approved vastly more dubious and worse takings.

However, there's no dispute government would then have to pay the entire fair market value for it, whatever anyone else would have to pay to buy the whole shebang right now. Novo as traded on the NYSE has a market cap of over $430 billion, and a sizable chunk of that is from this product which has sold well enough to measurably boost the entire Danish economy. The stock has nearly tripled in just the last year and half or so. Even if the US part of that one component was "only" 25%, $100b is not nothing, not even for the USG. And FMV might well be double or more.

There would be other legal avenues to explore but that's a big one, and in turn it's not actually clear it'd save the US any money which is kind of the point, eminent ___domain isn't supposed to be used that way but for some critical greater good. You can gain control but you have to pay for it.