Conor McGregor and Dustin Poirier were both drug tested once in the build-up to their UFC 257 clash with no adverse findings reported.
Poirier KO'd McGregor in the second round of their rematch last weekend to likely propel himself into a lightweight title shot.
And the UFC, through their partnership with USADA, have confirmed both athletes were tested in the build-up.
While only one test is listed for 2021, McGregor gave samples on eight occasions last year despite testing initially being scaled back due to the coronavirus pandemic.
Poirier who, like McGregor fought just once in 2020, was 10 times over the preceding 12 months.
The UFC and USADA announced their partnership five years ago with the agency providing an independent drug-testing for the athletes.
Fighters are signed up to the whereabouts system which requires them to inform USADA of their location.
Three sanctions have already been announced this year but USADA has also essentially eliminated marijuana use as a violation.
Athletes will not be punished unless it can be proved that the substance was used for performing-enhancing purposes.
And last month, the UFC's senior vice president Jeff Novitzky told ESPN : "I can't think of one instance in any historical cases where that evidence has been there.
"It would probably require visual signs if the athlete shows up at an event stumbling, smelling like marijuana, eyes bloodshot, things like that. And that's something you rarely, if ever, see. I certainly haven't in my six years with the UFC."
Despite his defeat by Poirier, McGregor wants an immediate trilogy bout - and for the title to be on the line.
He has targeted a return to the cage in May and is trying to convince the UFC he deserves another shot at Poirier.
If he fails, Nate Diaz and Tony Ferguson have been mentioned as alternative opponents.
