03/15/2013 07:00 EDT | Updated 05/15/2013 05:12 EDT

Can UFC welterweight Nick Diaz win Saturday, will he pass the drug test?

MONTREAL - The UFC's medicine cabinet has been wide open in the leadup to UFC 158 with marijuana, steroids and testosterone replacement therapy all front and centre.

Challenger Nick Diaz has tested positive twice for marijuana with his argument that he uses it medicinally to control social anxiety not carrying enough weight to sway the Nevada State Athletic Commission, which suspended Diaz for a year following his loss to Carlos Condit at UFC 143 in February 2011.

"I think I tested (positive) like for a metabolite or a nanogram or something, so it was like hardly," Diaz told Thursday's UFC 158 news conference.

"So I just did a little more than I did last time. I'm sorry if I don't pass the test," he added with a laugh, "But I think it should work out. I've passed plenty of them before."

White wasn't laughing, but said marijuana is anything but a performance-enhancer.

"I think it's the exact opposite. What the commissions are saying is they think it's a painkiller. Ridiculous. I don't believe in it. But here's the facts. It's illegal. You can't do it. It says it in the regulations you can't and if you get busted for doing it, you're going to be in big trouble. You're going to lose money, you're going to lose the ability to work for a year. So it is what it is and I just hope it doesn't happen on Saturday."

Asked what happens if Diaz does fail another drug test, the UFC boss replied: "It's not going to be good," suggesting he might have to be released.

The Quebec commission will handle drug testing for UFC 158.

Diaz's first positive marijuana test came in 2007 while he was fighting in Pride. He tried unsuccessfully tried to fight the second suspension in court.

The UFC cut welterweight Matt Riddle last month after a second positive test for marijuana, although White suggested there were other factors at work.

"He's a moron. That's why he's not here."

White seemed resigned that Diaz would continue to use marijuana.

"People are going to do what they're going to do," he said "I can't stop these guys. There's no difference than steroids or the TRT (testosterone replacement therapy). Let's just lump it all in the same (basket). It's like me trying to make Nick Diaz to stop smoking weed. How the hell am I going to do that? I can't.

"You know how many times I've talked to this guy? Even when we renewed his deal, I said 'Nick you can't test positive. Listen can you not smoke for a month, three weeks, whatever it is?' I'm not their father, man, I'm not their dad, I'm not the police."

Diaz later muddied the waters by accusing UFC welterweight champion Georges St-Pierre of being on steroids.

"I believe that he is on plenty of steroids and I don't think they test around here either," Diaz said in an interview with Sportsnet Radio on Thursday.

The doping issue had been raised when the two fighters got involved in a verbal exchange at the pre-fight news conference.

"I'm not on steroids," said St-Pierre. "I've never cheated in my life."

White also dismissed the drugs claim.

"He's never been busted for anything," he said of GSP. "The guy's fought a million times in title fights and mostly guys in title fights are the ones that get tested. He's never tested positive for anything even close."

In 2009, B.J. Penn also accused St. Pierre of taking steroids, although he said he had no proof.

"It's just my opinion that he uses steroids," Penn told Yahoo Sports. "That's it. My opinion. I do believe it. I can't hand you any proof, but that's my opinion."

As for TRT, White says he wants to lobby athletic commissions to stop allowing therapeutic exemptions for fighters on testosterone replacement therapy.

"If you have to use TRT, you're probably too old to be fighting," he said.

In the meantime, the UFC will test fighters who are on TRT.

"The guys who on TRT, their training camp is a lot easier than the guy who's all natural," White said. "The bangs, the injuries, all the (stuff) that goes on, they're recovering 10 times faster than the guy who's not doing it.

"So we're going to test these guys and make sure that that's not happening until TRT exemptions do not happen any more. ... We're going after the guys on TRT. The commissions test all these other guys."

Given the gruelling training that elite MMA fighters go through and the injuries they often sustain in preparing for fights, the temptation of taking something to get through such a grind is always there.

There is also financial pressure in that most fighters only get paid when they fight.

Fighters like Thiago Silva and James Irvin are among those who have tested positive, explaining that the drugs were offered a way to survive injuries or to help pay the bills.

And like all athletes, fighters are always looking for an edge.

Fighters are tested at UFC cards, with the organization contracting the testing in some areas where the local athletic commission doesn't. Major commissions like Nevada and California also do random out-of-competition testing.