The most common effects associated with antihistamines have been drowsiness sedation, dryness of mucous membranes, and gastrointestinal effects. Serious side effects with oral antihistamines or sympathomimetics have been rare.
Other adverse reactions may include:
Dermatologic - urticaria, drug rash, photosensitivity, pruritus.
Cardiovascular - hypotension, hypertension, cardiac arrhythmias, palpitations.
Central Nervous Systems (CNS) - disturbed coordination, tremor, irritability, insomnia, visual disturbances, weakness, nervousness, convulsion, headache, euphoria, and dysphoria.
Genitourinary - urinary frequency, difficult urination.
Gastrointestinal - epigastric discomfort, anorexia, nausea, vomiting, diarrhea, constipation. Respiratory - tightness of the chest and wheezing, shortness of breath. Hematologic - hemolytic anemia, thrombocytopenia, agranulocytosis.