According to a story first reported by Sports Illustrated and confirmed by the New York Times, baseball players in both the major and minor leagues have been warned to stop ingesting deer-antler spray.

The spray consists of “potentially contaminated nutritional supplements” and has been added to MLB‘s list of cautionary substances.

Manufacturers of the spray claim that it boosts “anabolic or growth stimulation,” “athletic performance” and “muscular strength and endurance.”