Local anesthesia can take anywhere from 1 to 4 hours to wear off, according to Caldwell Dental Care. Local anesthetics that are combined with epinephrine typically produce numbing effects for approximately 2 hours, while non-epinephrine anesthetics last a minimum of 1 hour.
Side effects of local anesthesia include inflammation or bruising at the injection site, vertigo, nausea and numbness of the skin, according to RxList. Severe side effects include convulsions, heart palpitations, vomiting, faintness and anxiety. Symptoms of an allergic reaction to local anesthetics include swelling of the face or tongue, breathing difficulties, hives and difficulty swallowing. Local anesthetics may also interact with medications like tranquilizers and antihistamines.