Major League Baseball has warned players of the "very real risk" of over-the-counter sexual enhancement pills which contain banned substances, according to media reports.

In a memo sent to major league and minor league players this week, MLB warned that "[s]exual or male enhancement products present a very real risk for drug-tested players and the high likelihood for contamination or unidentified ingredients in these products underscores the importance of consuming only those products that are NSF Certified for Sport."

ESPN, which obtained the memo, reported that use of the pills, which are often sold at gas stations, is so prevalent among players that MLB felt compelled to issue the warning.

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The league reminded players that they are subject to discipline should they test positive for banned substances. At least two players have blamed the pills after testing positive for performance-enhancing drugs. The names of the two players were not released.

"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," the memo said.

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

The memo suggested that players who “suffer from erectile dysfunction or other legitimate issues related to sexual performance … speak to a licensed physician about the various prescription medications available to treat those conditions.”