DENVER -- Daniel Stumpf said he rejoined the Phillies on Sunday with a clean conscience, maintaining his innocence and saying he has no idea how a performance-enhancing drug that first gained notoriety with East German athletes entered his system.
Stumpf, 25, tested positive in Spring Training for dehydrochlormethyltestosterone (DHCMT), which is an anabolic steroid better known as oral turinabol. He served the final game of his 80-game suspension Saturday. The Phillies activated him from the restricted list Sunday, optioning Severino Gonzalez and designating Mario Hollands for assignment to make room for him on the 25-man and 40-man rosters.
"I understand that it's going to be hard to believe for people," Stumpf said. "I understand that people say all the time that they don't know how it got into their system. I know that there's been chatter out there from people saying 'If you're taking an uncertified supplement, then you're taking the risk of that.' Well, I don't take supplements, period. I don't drink protein. I don't do pre-workout. I don't eat protein bars. I don't go to Smoothie King and drink smoothies, strictly because they mix stuff in their smoothies. The only thing I took in my life is fish oil because I had high cholesterol. That's the only supplement that ever went in my body."
East Germany developed DHCMT in the 1960s. It is ingested orally. It also is easily detectable.
Stumpf, who the Phillies selected in the 2015 Rule 5 Draft, said he tested positive for only one metabolite in his system.
"Everybody who gets caught says, 'Well, it's a metabolite in trace amounts,'" Dr. Stuart Phillips, a professor at McMaster University and an expert in exercise metabolism, told Sportsnet Canada, which reported on Toronto's Chris Colabello's suspension for DHCMT. "But everything's trace when you're measuring on that level. If you fail the test, and it's four parts per trillion, it means there's not very much of it in there. But there was none of it before.
"If you have a metabolite, then you had the drug in your system and you enjoyed the benefits of that drug at that time. You doped at some point. Whether you did it inadvertently or whether you did it deliberately is the question. But you still had it in your system."
Stumpf said he is still searching for answers. He has talked with Colabello, Triple-A Lehigh Valley pitcher Alec Asher, Mariners prospect Boog Powell and Minor League free agent Cody Stanley, who each have been suspended for DHCMT. 
"You might go take a drug test right now and have this M4 metabolite in your system," he said. "You don't know. Apparently it's not something that is created in your body. It's a synthetic thing so that's why they're saying that we have to have taken something. Other than food and a fish oil, that was the only thing in my body.
"If it could happen to me, it could happen to anyone."
Stumpf said he never appealed his suspension because he was advised it would delay the inevitable. He sent close to 60 items to be tested for possible contamination, including medications, cough drops, ChapStick and lotions. Each came back clean.
"I specifically told the union when I was going through this, I don't care if I have proof or not, I want to sit down in front of these people and I want them to tell me that I'm a liar, that I did this," Stumpf said. "I'm going to argue to you that I did not. They said that's not enough, that my word isn't good enough to them. So yeah, I was told I was going to lose, so I didn't appeal.
"I lay down at night with a guilt-free conscience. I know I didn't do anything. My family believes me. My teammates believe me. The Phillies believe me. God knows what I did. I don't have to prove myself to anybody. Obviously there's a bunch of guys in the game right now that are running their mouths now about this. And that's fine. But again, if this can happen to me it can happen to you."