United have said that they will appeal after a urine sample produced by Kenny taken after last May's play off game with Preston was found to include include traces of ephedrine.
Kenny was subsequently suspended by Sheffield United on June 4th and then banned by the FA on July 22nd
At an FA regulatory commission hearing on Monday, Kenny admitted the charge and was given a ban until April 22nd.
The substance was found in an over the counter medicine and Commission Chairman Chris Quinlan said: "Whilst we found that the player satisfied us, on the balance of probabilities, that the substance was not taken with the intention of enhancing sporting performance, his admitted conduct displayed significant fault.
"Mr Kenny knowingly ingested an over-the-counter medicine above the prescribed dosage without reading the accompanying package or leaflet and without reference to his club's doctor or other medical staff. To act in the way he did showed, in our judgment, a complete disregard for those responsibilities."
United boss Kevin Blackwell told the media: "Paddy is devastated and has gone home. "He has a lot to think about because he's banned completely from playing and training. I find it hard to believe the severity of the ban considering that it was accepted that the substance wasn't taken for performance enhancement. There's an appeals procedure and we will sit down and talk over the next few days and discuss the situation fully with all concerned.
"Let this be a warning to all players. They will be under the strictest scrutiny. And if they feel ill and reach for the medicine cabinet, they must be very sure that what they take doesn't contain any of the substances on the banned list, however innocently it might be taken."