The side effects of Fioricet are as follows:

dizziness
drowsiness
sleep problems
nausea
vomiting
abdominal pain
constipation
dry mouth
tremor
shortness of breath
lightheadedness
increased urination
weight loss
loss of appetite
jaundice
headache
feelings of being intoxicated
anxiety

Acetaminophen present in this medicine may cause a severe skin reaction in rare cases that can be fatal. Allergic reaction symptoms may include rash, itching or swelling, severe dizziness, and trouble breathing. Do not take this medicine again if you have this type of reaction.