Side effects cannot be anticipated for fioricet. If any develop or change in intensity, inform your doctor as soon as possible. Only your doctor can determine if it is safe for you to continue taking fioricet. More common side effects may include: Abdominal pain, dizziness, intoxicated feeling, light-headedness, nausea, sedation, shortness of breath, vomiting. Less common or rare side effects may include: Agitation, allergic reactions, constipation, depression, difficulty swallowing, dry mouth, earache, exaggerated feeling of well-being, excessive sweating, excessive urination, excitement, fainting, fatigue, fever, flatulence, headache, heartburn, heavy eyelids, high energy, hot spells, itching,muscle fatigue, numbness, rapid heartbeat, ringing in the ears, seizure, shaky feeling, skin redness sluggishness, stuffy nose, tingling.