Anthony Joshua and Kubrat Pulev both passed their final drug tests following their heavyweight clash last month.
Joshua stopped his mandatory challenger in the ninth round to retain his three world titles in London.
And the Voluntary Anti-Doping Ageny (VADA) has confirmed both fighters’ final samples came back clean.
Joshua insists his opponents enrol with VADA for a 10-12 week period before they meet in the ring.
That process saw Jarrell Miller miss out on a shot at the heavyweight world champion last year when he failed a drugs test.
Joshua instead fought Andy Ruiz Jr, losing in New York before avenging his defeat six months later in Saudi Arabia.
He was then forced to wait 12 months before returning to the ring due to the coronavirus crisis.
Joshua’s meeting with Pulev was initially scheduled for last June but instead took place three weeks before Christmas.
The Olympic champion had little trouble in front of just 1,000 fans at Wembley Arena however, dropping Pulev in the third round.
The Bulgarian survived and began to fight his way back into the bout before he was dropped twice in the ninth round.
The referee waved off the contest to ensure Joshua retained his belts.
He is now negotiating an undisputed fight with fellow world champion Tyson Fury with an announcement expected soon.
Promoter Eddie Hearn said recently: “We’re close. Backwards and forwards with contracts at the moment.
“Things have been progressing really well over the last week.
I really believe you will see that fight May/June, everyone’s working well in the right direction.”