Fighters must still avoid the drug on the day of the fight and are not permitted to use the drug for performance-enhancing reasons.
Both Nick and Nate Diaz have shared content on social media smoking the drug in recent years, while many others have fallen foul of the previous rules to incur a ban.
Niko Price, Kevin Croom, Tim Elliot and Jamahal Hill have all been temporarily taken out of the sport due to marijuana use.
However, different commissions could still impose a ban depending on local authorities’ regulations.
Senior vice president of athlete health and performance for the UFC, Jeff Novitzky, said: “While we want to continue to prevent athletes from competing under the influence of marijuana, we have learned that blood and/or urine levels of carboxy-THC have little-to-no scientific correlation to impairment.
“THC is fat soluble, meaning that once ingested, it is stored in fatty tissues and organs in the body and can be released back into the blood or urine, sometimes long after ingestion.
“The bottom line is that in regards to marijuana, we care about what an athlete consumed the day of a fight, not days or weeks before a fight, which has often been the case in our historic positive THC cases.”
Novitzky also warned fighters to “temper their enthusiasm” due to the uncertainty surrounding rules with various commissions.
While education on the drug is high on the UFC’s priorities right now and there could be experiments in the future with psychedelic drugs to treat traumatic brain injuries, including those suffering from CTE (Chronic Traumatic Encephalopathy).