The league has a marijuana problem, and the league knows it.
At a deeper level, the NFL knows that a straight-faced excuse for persisting in the pot prohibition must be articulated in conceal the real reason for it: Collective bargaining.
Marijuana has 2 compounds, THC which is what get you high, and CBD, which is the actual painkilling compound.
THC can be psychologically addicting but is not physically addictive.
CBDs do not get you high, and have zero addictive properties.
The league should let players use CBD products for painkilling and not allow the THC products if they feel that strongly about it.
http://profootballtalk.nbcsports.com/2017/05/02/nflpa-continues-to-focus-on-marijuana-for-therapeutic-reasons/