Despite passing his UFC 202 in-competition drug tests, Nate Diaz may still face disciplinary action after admitting to vaping CBD oil during the post-fight press conference.

Diaz, who suffered a majority decision loss to Conor McGregor at the T-Mobile Arena last month, fielded questions from reporters after the bout and was asked what he was vaping.

"It's CBD," he replied. "It helps with the healing process and inflammation, stuff like that. So you want to get these for before and after the fights, training. It'll make your life a better place."

Cannabidiol is one of 113 active cannabinoids contained in cannabis.

Cannabinoids are banned by the WADA Code in-competition and includes the six hours leading up to the fight as well as the six hours proceeding it. The post-fight press conference falls within this remit. 

WADA spokesperson Ryan Madden told MMA Fighting that USADA would be investigating the matter.

"I can confirm that USADA is aware of the situation and is currently gathering information in order to determine the next appropriate steps," he said. 

Cannabis is not an anabolic steroid or hormonal agent, but it is still prohibited in certain cases, like in-competition. It is considered a "specified substance" and should Diaz be found guilty he could face up to a one-year ban by USADA.