Yes. Any medication can cause problems if taken in excess. Though I am not familiar with specific symptoms regarding Allegra (fexofenadine) overdose, most of the time, patients will have vomiting, abdominal pain, or headaches. I would imagine that liver problems might occur with too much Allegra (fexofenadine) as it is a medication that is broken down by the liver. Bottom line: don't do it.