Frequently Observed: The most frequently reported adverse reactions are drowsiness, lightheadedness, dizziness, sedation, shortness of breath, nausea, vomiting, abdominal pain, and intoxicated feeling. Infrequently Observed: All adverse events tabulated below are classified as infrequent. Central Nervous: headache, shaky feeling, tingling, agitation, fainting, fatigue, heavy eyelids, high energy, hot spells, numbness, sluggishness, seizure. Mental confusion, excitement or depression can also occur due to intolerance, particularly in elderly or debilitated patients, or due to overdosage of butalbital. Autonomic Nervous: dry mouth, hyperhidrosis. Gastrointestinal: difficulty swallowing, heartburn, flatulence, constipation. Cardiovascular: tachycardia. Musculoskeletal: leg pain, muscle fatigue. Genitourinary: diuresis. Miscellaneous: pruritus, fever, earache, nasal congestion, tinnitus, euphoria, allergic reactions. Several cases of dermatological reactions, including toxic epidermal necrolysis and erythema multiforme, have been reported. The following adverse drug events may be borne in mind as potential effects of the components of this product. Potential effects of high dosage are listed in the OVERDOSAGE section. Acetaminophen: allergic reactions, rash, thrombocytopenia, agranulocytosis.