Along with its needed effects, acetaminophen/butalbital (Fioricet)/caffeine may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.
Check with your doctor immediately if any of the following side effects occur while taking acetaminophen / butalbital (Fioricet) / caffeine:
More common
•    Lightheadedness
•    shortness of breath
•   Incidence not known
•    Abdominal or stomach pain
•    black, tarry stools
•    bleeding gums
•    blistering, peeling, or loosening of the skin
•    blood in the urine or stools
•    blurred vision
•    change in the frequency of urination or amount of urine
•    chills
•    cough
•    diarrhea
•    difficulty with breathing
•    difficulty with swallowing
•    dizziness
•    drowsiness
•    dry mouth
•    fainting
•    fast, pounding, or irregular heartbeat or pulse
•    flushed or dry skin
•    fruit-like breath odor
•    hives, itching, or skin rash
•    increased hunger
•    increased thirst
•    increased urination
•    joint or muscle pain
•    loss of appetite
•    nausea or vomiting
•    pinpoint red spots on the skin
•    puffiness or swelling of the eyelids or around the eyes, face, lips, or tongue
•    red skin lesions, often with a purple center
•    red, irritated eyes
•    seizures
•    shakiness in the legs, arms, hands, or feet
•    sore throat
•    sores, ulcers, or white spots in the mouth or on the lips
•    sweating
•    swelling of the feet or lower legs
•    tightness in the chest
•    trembling or shaking of the hands or feet
•    troubled breathing
•    unexplained weight loss
•    unusual bleeding or bruising
•    unusual tiredness or weakness
•    weakness