Arguably the monopoly is intrinsic: pharma companies have the pre-existing ability to hide the product of their R&D, e.g. by only selling it in closed clinics, or by obfuscating pills with thousands of inert ingredients ("DRM for wetware"). In this view, monopoly rights are granted to extract the social benefit of public disclosure. (And "disclosure" still minimal and ineffective: pharma is massively secretive about their research -- rationally -- which certainly isn't globally optimal).
And the goverment by the virtue of having tanks and jets and soldiers has intrinsic monopoly to decide what are the rules that have to be observed to even be allowed access to the market of given country.
The companies can move to another country. One with more nuclear bombs! And force the people from the other country to travel if they want the treatment.
Yes, you can migrate to country with fewer rules and not operate on other markets. Like a brothel with underaged prostitutes that people from other countries travel to to buy services disallowed on their native markets.
In practice it doesn't work that great. Stronger countries with richer customers tend to use their leverage and have more rules. It definitely works for illegal products but I doubt it would work for goods that are legal but coming from manufacturer who's illegal. Goods would got cloned by legal manufacturers pretty quick if they were so good they'd be worth traveling for.
