The league said he tested positive for Growth Hormone Releasing Peptide-2 (GHRP-2).
Collins told ESPN's Adrian Wojnarowsi that he plans to appeal the suspension, which was set to begin Tuesday night when the Hawks host the San Antonio Spurs.
"First I want to apologize to my teammates, the Hawks organization, our fans, partners and community as a whole for this situation," Collins said in a statement to Wojnarowski. "I understand the impact this matter has on what we are trying to achieve together this season, and I am incredibly frustrated and disappointed in myself for putting all us in this position.
"I have always been incredibly careful about what I put in my body, but I took a supplement, which unbeknownst to me, had been contaminated with an illegal component. I plan to appeal my suspension in arbitration so I can get back on the court as soon as possible and continue to contribute to our 2019-20 campaign."
The 22-year-old is in his third NBA season and is part of a young nucleus for the improving Hawks, which includes second-year guards Trae Young and Kevin Huerter, as well as rookie Cam Reddish. The Hawks made Collins, a Wake Forest product, the No. 19 overall pick in the 2017 draft.
In 140 career games (90 starts), he is averaging 14.6 points and 8.4 rebounds per game. In five games this season, he is averaging 17.0 points and 8.8 rebounds per game and shooting 47.4 percent from 3-point range.
"On behalf of the entire Hawks organization, we are disappointed to learn that John put himself in an unfortunate situation and violated the league's anti-drug policy," the Hawks said in a statement. "We hold ourselves and each of our players to a high standard, and we are committed to supporting John as he learns from this setback and continues to grow as both a player and a person. Head Coach Lloyd Pierce and I have both talked to him and we believe that he is truly remorseful for his actions. We will provide John with support on and off the court while we look forward to his return to the team."
--Field Level Media