On January 13, 2016, Romero was informed of a potential doping violation stemming from an out of competition test conducted by USADA. On February 8, Romero and his manager explained that he had taken a supplement after his fight that turned out to be contaminated. His team and USADA both sent out the supplement for testing and it was confirmed that it contained a banned substance. That substance was not listed on the label, his manager said. They did not want to reveal the name of the supplement or the substance, because USADA was investigating the issue. On March 23, it was announced that Romero would appeal his suspension. His team and USADA discussed a deal for a nine-month suspension for the fighter, but Romero preferred to go to arbitration. The typical USADA anti-doping violation suspension is two years. Eventually on April 4, both parties reached an agreement for a six-month suspension. USADA revealed that Romero tested positive for ibutamoren, a growth hormone release stimulator. An unopened version of the supplement was independently tested and the banned substance did indeed come up, even though it was not listed on the label. Romero announced that he would pursue legal action against the supplement company. The result of the Souza fight was not overturned, as it was an out-of-competition test that occurred after the fight; Romero passed both his pre-fight and fight night tests for the Souza fight.