The Electronic Sports League (ESL) said Thursday it will begin policing against substances that could improve an eSports competitor’s playing ability after Kory “Semphis” Friesen, one of its top athletes, admitted to using Adderall in a major tournament earlier this year.

The first step in that policing will be randomized skin tests at the league’s One Cologne event next month.

“The growing visibility and popularity of eSports, as well as increasing prize pools make it not only more tempting for teams and players to break the rules, but also more damaging to our sport as a whole when they do,” the ESL said in a statement. “ESL has an ongoing commitment to safeguarding the integrity of our competitions and providing a fair playground for professional players. With this in mind, today we’re announcing further steps our organization is taking, to determine and enforce guidelines and rules the use of performance enhancing drugs (PEDs) at ESL events.”

The ESL did not specifically name the drugs that would be banned or tested for, saying the list is still being compiled. The group, however, is almost certain to forbid the unprescribed use of ADHD drugs like Adderall and Ritalin, amphetamines some players use to sharpen their focus, which can help in the extraordinarily fast-paced games.

Adderall has quickly become the drug of choice for many teens and young adults who hope to better focus on tasks in recent years. A 2014 study by the National Institute on Drug Abuse (NIDA) found that nearly 7% of high school seniors had used the drug without a prescription. Ritalin, which is another stimulant used to treat ADHD, was used much less frequently, with less than 2% saying they took the drug without a prescription.

Its use in eSports has been widely speculated for years—with many outlets reporting it is commonplace. ESL officials, though, say they’re not sure how accurate those reports are.

“It is difficult to determine without tests,” Michal Blicharz, managing director of progaming for ESL, told Fortune. “Several years ago, PEDs had marginal use in eSports. In the last 18 months, the industry accelerated so quickly that players are earning literally ten times what they were earning [previously] and the prize purses go into millions. Barring [Friesen’s] interview, we have no knowledge of players using PEDs, but we are recognizing that the temptation to cheat is higher than ever and that we need to take measures to educate, prevent this from happening and punish players if we have to.”

Headquartered in Cologne, Germany, the ESL is the oldest and one of the largest eSporting leagues in the world. Earlier this month, Swedish media company Modern Times Group bought a majority stake in the group for $87 million.

Its rules on PEDs could trickle down to other eSports groups in the months to come, but none immediately rushed to match the announcement. A representative for Major League Gaming, who earlier this year partnered with ESPN to include its competitions in the X Games, said the company already has policies regarding prohibited drugs in their code of conduct and does not plan to begin testing athletes at this time.

The NCAA, the MLB, and the NFL have all previous forbidden players from using Adderall. Last year, Baltimore Ravens defensive end Haloti Ngata was suspended for the final four games of the regular season after testing positive for Adderall without having a waiver to use the drug.

The ESL’s decision to crack down on performance enhancing drugs is still nascent, though. The league is still determining the methods it will use to test for the substances on a permanent basis and has not yet detailed the disciplinary actions for players that fail those tests.

To underscore its seriousness about the matter, though, the ESL said it has partnered with Germany’s Nationale Anti Doping Agentur (NADA) to research and determine a final policy—and plans to meet with the World Anti Doping Agency (WADA) to bring it into the process as well.

“The goal of this program is to ensure players are provided with information and structural support to help them manage the physical and emotional pressure that the highest level of competitive gaming puts on many of them,” the ESL said.