"We know from experience that a number of these sexual or male enhancement products—which are sold online, at retail stores, and on the black market, both in the United States and internationally—contain anabolic steroids and other prohibited substances.

"For this reason, we strongly urge players against taking any sexual or male enhancement product, from any source."

Major League Baseball did note, however, that players suffering from erectile dysfunction or other sexual performance issues consult a "licensed physician about the various prescription medications (e.g., Viagra, Cialis, Levitra) available to treat those conditions."

The Food and Drug Administration also warned in February that a number of over-the-counter dietary supplements and sexual enhancement pills often contain "hidden active ingredients that could be harmful" and that "consumers may unknowingly take products laced with varying quantities of approved prescription drug ingredients, controlled substances, and untested and unstudied pharmaceutically active ingredients."

One of the common defenses MLB players have used in the past when facing a suspension from baseball is that they didn't realize a supplement they were taking would trigger a failed drug test under the league's performance-enhancing drug policy. Given this latest memo from the league, that excuse—at least regarding sexual-enhancement drugs—likely won't hold much water.