There are multiple effects:
- The balloon effect - if eg. Australia or the EU does price fixing, the balloon gets squeezed on their end, and bulges on the US end. This is what Trump is trying to avoid by mandating the preferred country - so costs for Australians, Brits and other Europeans are going to increase because we're no longer subsidizing their healthcare (which the US currently does for billions per year).
- The invention effect - many drugs available in the US are recently invented and not available in other markets, so the average price is high because we are paying thousands for new 'luxury' drugs like Ozempic. Eg chemotherapy used to be such 'luxury' treatment, when rich Americans started treating cancer, it eventually became available everywhere.
- The cherry picking effect - when news organizations cherry pick data on specific drugs and treatments, you get some weird numbers. However, the US pays lower prices on average for about 80% of drugs (generics) compared to other countries who pay on average more per dose for generics. On the other hand statistics from other countries often do not include private healthcare costs. Eg. in most countries a not insignificant amount of people still requires/desires private health care, which is significantly more expensive than the US (hence why people come TO the US for health tourism and besides some sketchy procedures, nobody goes to Canada or Mexico) and not included in public cost schedules.
- Simpson's paradox - Most data about medical care needs to be classified in a category and then you can compare categories. Eg. it makes no sense to compare cancer care survival rates and costs if a country like Canada or some EU countries promotes euthanasia as a cost reduced option but does not consider it an adverse effect. So if you're aggregating 20% of treatments that aren't available in other countries, aggregating dissimilar data and make sweeping statements, you end up with huge errors.