Nitazoxanide typically starts working within a few days of initiating treatment. As an antiparasitic and antiviral medication, its onset of action varies based on the specific infection being treated. For parasitic infections like giardiasis or cryptosporidiosis, symptoms often improve within a few days, though completing the full course is essential. In viral infections, like some cases of influenza or respiratory syncytial virus (RSV), nitazoxanide may help reduce the duration and severity of symptoms. However, individual responses can vary, and it's crucial to follow healthcare provider recommendations for the prescribed duration and dosage for optimal effectiveness.