I think the key point I would like to make is that you have to design a regulatory framework that compels and actually mandates the manufacturer to complete phase four, or post-marketing trials. The penalty would be withdrawal of the product from the market. Several countries, like the United States, France, the United Kingdom, Australia, and New Zealand, have all tried various regulatory frameworks using various forms of suasion other than strict regulation, to encourage firms to engage in these post-market studies. A significant majority of the studies never get completed.
In New Zealand, they created legislation allowing the medical regulatory agency to commission their own studies of post-market safety and effectiveness for medicines. It commissioned those studies to independent academic groups to ensure they were completed in a public and transparent way.
That appears to be New Zealand's solution to the difficulty of compelling a business to complete a study. In some sense, if the regulatory framework says once it's on the market, it's on the market; it's not in the businesses' interest. That's not to blame firms; that's just the nature of business.
We need to change the regulatory framework to either make regulatory requirements subject to withdrawal or to say that the government will engage in the studies and adequately fund the studies to ensure they're completed.