ADVERSE REACTIONS Transient drowsiness, the most common adverse reaction associated with clemastine fumarate, occurs relatively frequently and may require discontinuation of therapy in some instances. Antihistaminic Compounds It should be noted that the following reactions have occurred with one or more antihistamines and, therefore, should be kept in mind when prescribing drugs belonging to this class, including clemastine. The most frequent adverse reactions are italicized. 1. General: Urticaria, drug rash, anaphylactic shock, photosensitivity, excessive perspiration, chills, dryness of the mouth, nose, and throat. 2. Cardiovascular System: Hypotension, headache, palpitations, tachycardia, extrasystoles. 3. Hematologic System: Hemolytic anemia, thrombocytopenia, agranulocytosis. 4. Nervous System: Sedation, sleepiness, dizziness, disturbed coordination, fatigue, confusion, restlessness, excitation, nervousness, tremor, irritability, insomnia, euphoria, paresthesias, blurred vision, diplopia, vertigo, tinnitus, acute labyrinthitis, hysteria, neuritis, convulsions. 5. GI System: Epigastric distress, anorexia, nausea, vomiting, diarrhea, constipation. 6. GU System: Urinary frequency, difficult urination, urinary retention, early menses. 7. Respiratory System: Thickening of bronchial secretions, tightness of chest and wheezing, nasal stuffiness.