Numb tongue was a condition that presented itself during an allergic reaction to medicine.
In 2258 of the alternate reality, Cadet James T. Kirk began to suffer from numb tongue as a direct result of medication given to ward off the symptoms of the Melvaran mud flea vaccine that Doctor Leonard McCoy had administered to him. Kirk attempted to warn Lieutenant Nyota Uhura that the Enterprise was heading into a trap laid by Nero at Vulcan, but his condition prevented him from speaking to her clearly. McCoy gave him another hypospray of something else to counteract the frustrating side effect. (Star Trek)