Cannabis has been medically prescribed in CO for nearly 20 years. As of this year, autism spectrum disorders are a disabling medical condition qualifying for medical use, joining PTSD, seizures, cancer, glaucoma, AIDS, severe pain, and others.

https://www.cell.com/pb-assets/journals/trends/molecular-med... draws similar conclusions scientifically rather than anecdotally -

"Currently, science does not support the development of cannabinoid limits in motor vehicles drivers per se because of the many factors influencing concentration–effect relation-ships."

"There is no one blood or oral fluid concentration that can differentiate impaired and not impaired."

I'm not sure what you're on about, prescriptions for marijuana are a thing...