The UFC star marked the annual marijuana holiday, which takes place every year on April 20th, by posting a snap of him lounging on a couch while blowing out a cloud of smoke.
“Happy 420 day,” he wrote as he added a shamrock emoji alongside a gust of wind emoji.
The Dubliner revealed last year that he owned a hemp farm in Eugene, Oregon, which he claims is the “best hemp farm in the USA.”
Responding to an Instagram comment at the time, he said: “The strain is indica dominant. A lovely strain! It comes from my hemp farm in Eugene, Oregon. Where my @tidlsport is produced.
“We've been testing some different strains out. This one is indica dominant, but we've a lot of quality produce in the works for our fans.
“The land around Oregon, and Eugene in particular, is absolutely breath-taking. I've the best hemp farm in the USA. Produces nothing but quality!
“A few hits of this one to unwind and enjoy the sounds and the surrounds. Works a real treat with my recovery too. Everything in moderation though. God bless.”
The hemp is used in McGregor's TIDL Sport Plant-Powered Cryotherapy Topical Spray, which he launched last year.
The 33-year-old's 420 tribute comes as he prepares to return to action at welterweight in the summer after suffering a devastating leg break during his bout against Dustin Poirier last July.
He has been training at Crumlin Boxing Club as in preparation for his grand return to the sport later this year and is hoping to become the first ever fighter to win titles at three different weights in the UFC.
“I’ve already won the 155lb title. I got myself down to a lightweight frame, but I’m big now. I feel strong, I feel healthy, I’ve got good energy. I’m coming back after a gruesome injury. I do not want to deplete myself, there should be no need to deplete myself,” he told MacLife.