Medical pot was by prescription and not one of these new pot companies whose stock is so affected.
No, it is about stocks regarding the entire industry - not just dispensaries - as explained in the article.
“In December 2014, however, the Rohrabacher–Farr amendment was signed into law, prohibiting the Justice Department from prosecuting individuals acting in accordance with state medical cannabis laws.[126]”
https://en.m.wikipedia.org/wiki/Medical_cannabis
Medical use will still be allowed.