That, of course, is the banned substance that Ruiz was using, as first reported by The Inquirer, when he was hit with a 25-game suspension that he served at the start of the 2013 season. He is not the first player to receive an exemption for the amphetamine, which is used to treat people with ADHD - attention-deficit hyperactivity disorder.
Neither Ruiz nor the team has ever admitted publicly that Adderall was the banned substance that caused Ruiz's suspension.
In fact, he is among a growing number of major-league players with an exemption. According to a joint release by MLB and the Players Association in November, a record total of 122 therapeutic exemptions were granted last season, including 119 for ADHD. That number is a controversial one because it means that roughly 10 percent of major-league players have a diagnosis of ADHD, much higher than the 4.4 percent reported among the United States' general population.
Regardless, the fact that Ruiz is again able to get the help he believes he needs is good for the Phillies.
"I don't want to talk about that," Ruiz said before the Phillies' first full-squad spring training workout of the Ryne Sandberg era. "I'm fine and I feel great. I know it was reported, but that's something that is personal. I'm great now."
It's understandable that Ruiz does not want to talk about it. Former Phillies centerfielder Shane Victorino, who also requires medication for ADHD, exercised the same philosophy.
There's no position on the field, however, that would be more adversely affected by ADHD than catcher. They are the players responsible for running the pitching staff and calling the pitches, and they must be ready to catch every pitch. Add in the fact that catchers get nicked by countless foul balls throughout the season and it is easily the most dangerous and demanding position on the field.
One thing is clear at the start of this spring training: Ruiz is in a lot better state of mind than he was a year ago at this time, and that's great news for the Phillies.
The scene just beyond the left-field wall at Bright House Field last February was a painful one to witness. Ruiz had only himself to blame for the 25-game suspension, but his teary-eyed apology was heartfelt and his extended absence at the start of the Phillies' disastrous 2013 season was a gut punch to the team and the catcher.
"Yeah, it was, but I've put that behind me because what happened is over," he said.
By the time Ruiz returned on a Sunday afternoon in New York last season, the Phillies were 11-14 and in fourth place in the National League East, which is where they would eventually finish. The catcher, no longer able to use Adderall and only able to play in five minor-league games before rejoining the team, struggled out of the gate after arguably being the team MVP in 2012.
And then things went from bad to worse. He was hitting .235 with two extra-base hits and two RBIs when he landed on the disabled list May 20 with a strained right hamstring. He didn't return until June 18.
The truth of the matter is that the Carlos Ruiz who made his first all-star team at the age of 33 in 2012 never did return last year. He did have a 61-game stretch from June 26 to Aug. 14 during which he hit .305 with five home runs and 31 RBIs, but that was his only prolonged period of solid play. The Phillies were 30-31 during that time period, which is proof they had a lot of other issues besides the catcher.
Still, the catcher's extended absences and inability to duplicate his play from the season before ranked among the top three reasons the Phillies fell to fourth place in the National League East. He started just 83 games. Add in the fact that Howard played only 80 games and you had two key players who were half themselves playing only half the time.
Get those two at 100 percent for an entire season and vast improvement is a feasible conclusion.
"People can think whatever they want," Ruiz said. "That's OK. Like I said, I believe in this team and we'll see what happens when the season starts. That's the time when you can talk. We have some guys here who know how to play baseball and have talent."