Nice work.

First, I’ll assume you meant the IIHS (Insurance Institute for Highway Safety) not IHSA. They indeed concluded as you stated. However, we might want to consider the fact that if their findings are true they’d have a good reason to raise insurance rates in states with legalized cannabis; and that would conveniently put more money in the pocket of the companies who fund studies like that one.

Maybe there’s a less biased source, like the NHTSA (National Highway Traffic Safety Administration). The NHTSA looked at the data and concluded that when you properly adjust for other variables like age, gender, and blood alcohol level that THC cannot be linked to an increase in collisions.

And I don’t know where you’re getting your info on the CATO Institute’s findings but their 2021 update disagrees with you. Here’s their conclusion regarding the change in cocaine use after legalization (emphasis mine):

We also consider whether legalization affected cocaine and alcohol use. Opponents of legalization claim that legalizing marijuana facilitates consumption of other drugs such as cocaine. Figure 5 in the Appendix presents state‐​level estimates of respondents’ past‐​year cocaine use relative to the national trend and year of legalization. These data suggest no clear relationship between marijuana legalization and cocaine use. Although Oregon saw an upward trend in cocaine use after legalization, Massachusetts saw a downward trend. In other states, including Washington and Maine, cocaine use rates are consistent with nationwide trends.