It takes decades and hundreds of millions of dollars in order to build a statistical argument that explains likely effects, side-effects and risks of prescribing that drug to the population at large.

It takes that long and costs that much because there is no safe way to do this with human physiology other than to carefully, slowly and expensively try it and measure the consequences.

We can take any AI system and model its behaviour with statistical certainty much more cheaply and quickly, and be more confident in its future behaviour.

Remember, AI and ML are fancy words for some form of a regression to a mean more often than not. If we run hundreds of millions of tests of such a system in simulation for a very wide range of contexts/inputs (which is cheap to do), we can have a much higher degree of confidence in a short space of time around behaviour of that system than we will for any drug test, even if we still don't fully understand the causality.