A middleweight bout between Arizona Combat Sports fighter Steve Steinbeiss and UFC veteran Ryan Jensen has been canceled for Wednesday night's UFC Fight Night 18, as confirmed by UFC.com

In a statement received by MMAWeekly.com, UFC officials said the fight was off "due to a medical approval issue regarding (Ryan) Jensen."

Questions about the fight were raised during the weigh-ins on Tuesday when Jensen and Steinbeiss did not come out with their fellow athletes during the customary event. They did appear about 15 to 20 minutes later with both fighters weighing in at 186 pounds.

Independent sources have confirmed to MMAWeekly.com that the alleged medical issue stems from Jensen's use of Adderall, which is not allowed under standard athletic commission rules.

According to drugs.com, "Adderall is a central nervous system stimulant. It affects chemicals in the brain and nerves that contribute to hyperactivity and impulse control.

"Adderall is used to treat narcolepsy and attention deficit hyperactivity disorder (ADHD)."

According to sources, Jensen disclosed his use of the drug to the commission and the bout was held up pending further approval. Obviously, the commission decided to scrap the bout all together, and Jensen vs. Steinbeiss will no longer happen ... at least in Nashville, Tenn., Wednesday night.

A similar situation to this happened at The Ultimate Fighter 7 season finale when Tim Credeur admitted to using the same drug, Adderall, and the Nevada State Athletic Commission canceled his scheduled bout against Cale Yarbrough in much the same manner.

That evening, Commission Executive Director Keith Kizer said Adderall "acts as a cardiovascular restrictor and that's the main reason it's banned because it can cause athletes to have a cardiac episode with the stress they're under when they're in an athletic competition. Secondly, it can have a performance-enhancing effect as well."

Credeur was not fined or suspended for his infraction, but it is not known at this time if Jensen will face any disciplinary action from his admission with the Tennessee Athletic Commission.

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