Lexapro Side Effects. Common side effects of Lexapro include: headache, drowsiness, diarrhea, nausea, ejaculatory disorder, insomnia, and delayed ejaculation. Other side effects include: fatigue, constipation, dyspepsia, anorgasmia, dizziness, xerostomia, decreased libido, and diaphoresis. See below for a comprehensive list of adverse effects.