I've heard of this argument before but I think it really needs some evidence. Is there a study that corroborates this claim? Even if the US really "subsidizes"

I've heard of this argument before but I think it really needs some evidence. Is there a study that corroborates this claim? Even if the US really "subsidizes" medicine for the rest of the world, what motives do pharmas have to sell medicine at lower-than-production/R&D-cost to the rest of the world? Couldn't they just sell to the US exclusively, let the rest of the world rot, and then sit on a bigger pile of cash as a result?