Hi, Nasal spray works by modulating the adrenergic receptors to stimulate the nor-epinephrine (it is a neurotransmitter at the end of certain neurons) present in your nasal mucousa, which then results in vasoconstriction in the mucousal bed, causing the mucousa to shrink, which in normal life, is how you feel great when your nose stops running. But then, as your granny often tells you that excess of everything is bad, nasal spray is no exception. Prolonged use, often for more than 3 days, results in down regulation of the same receptors and withdrawal of nor-epinephrine from the adrenergic sites, possibly by rapid internalisation of the receptors, degradation and subsensitivity, called tachyphylaxis in our scientific parlance. Clinically this manifests as reduced response to your medication and rebound of your symptoms. How to prevent this from happening? Do not use for long periods continuously. Follow your doctor s advice. Since the medication works on α receptors, albeit mostly topically in your nasal mucousa, it can also cause side-effects related to stimulation of these receptors, especially in the vulnerable. Systemic hypertension (a 5$ word for increased blood pressure) because of systemic vasoconstriction. Urinary flow obstruction, especially in those prone to developing benign prostatic hypertrophy. Other more manageable side effects may include sleep disturbances, dizziness, psychological issues like excitation and nervousness, atrophic rhinitis and anosmia, nausea, etc. Hope I have answered your query. Let me know if I can assist you further. Regards, Dr. Ajeet Singh, General & Family Physician