BJ Penn's comeback has been a rocky road since he announced that he was coming out of retirement to fight in the UFC once again.

First, Penn faced allegations of assault against an ex-employee's girlfriend, although charges were never filed and an investigation done by the UFC allowed him to return to work where he booked his next fight.

This latest incident involved an IV treatment that Penn took back in March around the same time that he was tested by the United States Anti-Doping Agency (USADA) on behalf of the UFC.

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Athletes are banned from using IV's because the treatment could be used to "manipulate their plasma volume levels in order to mask the use of a prohibited substance and/or to distort the values in the Athlete Biological Passport," according to the USADA code.

Penn disclosed the IV usage to USADA and because it was over the 50mL limit in less than six hours, he was removed from the UFC 199 fight card and his bout with Cole Miller was cancelled.

"I wasn't aware that I couldn't take an IV 365 days a year," Penn said when speaking to KHON2 in Hawaii. "I got an IV back in March, and USADA came to do a test. We did the test and they asked me when was the last time I got an IV, and I said oh, the week before, and that's it.

"We're not being investigated for any banned substances or nothing like that. It's just I disclosed to USADA that I did an IV without getting permission from them first, and they penalized me for it."

It's unclear why Penn reported the IV use back in March but only now is facing a potential suspension as a result of the illegal infraction.

Penn is provisionally suspended pending a judgment being rendered at a later date by USADA, and the former two-division champion also has the right to an appeal hearing.

"I don't think it should be too long, because, I mean, ignorance of the rule is no excuse, but if it has nothing to do with banned substances, we're not doing anything with any performance enhancement, and I think they just gotta lay down the punishment for whatever they feel," Penn said.

There's no word on what kind of suspension Penn might face as a result of the drug testing snafu that cost him the fight at UFC 199.

Penn clearly doesn't expect a lengthy suspension, and he promises that this setback won't stop him from returning to the UFC once he's allowed to fight again.

It's merely another roadblock he has to hurdle.

"It's just got to be a speed bump, but I've went way too far to say I'm exhausted at this point. It's amazing how my fights have just been getting pushed back," Penn said. "I guess this is just one more road bump, and I'm the best I've ever been. I'm doing great in the gym. I feel awesome.

"I don't think Greg Jackson would let me quit at this point. It's just amazing the way this all went down."