As part of the MLB's efforts to crack down on opioid use in and around its league ... it has agreed to stop testing minor leaguers for weed, The Athletic's Ken Rosenthal reports.

Of course, the MLB already didn't test its big leaguers for marijuana ... but the rule change for everyone else is a big deal for the sport.

Previously, minor league players faced a 25-game suspension for a first positive weed test, a 50-game suspension for a second test, a 100-game suspension for a third and a ban for LIFE for a fourth.

Ex-Milwaukee Brewers relief pitcher Jeremy Jeffress is among the list of several current MLB players who have previously been popped for using weed in the minors.

As for the why now ... MLB officials are clearly trying to deter players from turning to opioids to fix their issues -- this after Angels pitcher Tyler Skaggs tragically died from an accidental overdose on fentanyl, oxycodone and oxymorphone this past year.

MLB still lists dozens of recreational drugs on its banned substance list ... including cocaine, LSD and MDMA.