Theraflu is generally not recommended during pregnancy without consulting a healthcare provider, especially due to one of its common ingredients, phenylephrine. Phenylephrine can constrict blood vessels, potentially reducing uterine blood flow and oxygen to the baby, and may cause high blood pressure in pregnant women. While some other ingredients in Theraflu, like acetaminophen and diphenhydramine, are considered relatively safe when used short-term, the presence of phenylephrine raises concerns, especially in the first trimester. Therefore, it is advised to speak with a healthcare provider before taking Theraflu while pregnant to weigh the risks and benefits for your specific situation and consider safer alternatives for symptom relief.