Four pitchers have tested positive for the steroid Stanozolol since baseball season began. Major League Baseball (MLB) is trying to figure out why the drug, long popular with bodybuilders, may have made a comeback, USA Today reports.

According to the Daily News, MLB investigators have launched an investigation to determine if there is a link between the four cases, such as a trainer, doctor, dietary supplement or drug dealer.

Stanozolol, which is sold under the brand name Winstrol, is easily detectable on drug tests. It stays in the system for weeks or even months after it is used.

The four players who have been suspended for 80 games are David Rollins of the Seattle Mariners, Arodys Vizcaino of the Atlanta Braves, Ervin Santana of the Minnesota Twins and Jenrry Mejia of the New York Mets. Last year, only three players were penalized for using performance-enhancing substances.

MLB suspended 13 players in 2013 for drug-policy violations, but none were caught by drug testing.

Speaking of Mejia’s suspension, Mets Manager Terry Collins told reporters, “It happens in the business, but it’s a damper. I understand everything about it, I really do, but you know what? There are 24 other guys in that locker room that need him, too. That’s why it is so disappointing.”