Whether or not acetylcysteine can be used for a long time, or for how long, should be applied as prescribed by your doctor. This medication is generally not recommended for long-term use. Acetylcysteine is mainly used for the treatment of phlegm in respiratory diseases such as chronic bronchitis with thick mucus secretions, bronchiectasis, emphysema, etc. Long-term use is generally not recommended. Prolonged administration may cause adverse reactions such as nausea, vomiting, bronchospasm, allergic reactions, angioedema and so on. It is contraindicated for those who are allergic to the drug and its components. It should be used with caution in patients with a history of bronchospasm, bronchial asthma, gastric ulcers and so on. If the condition requires long-term use of the drug, it should be taken in accordance with medical advice and regular treatment under the guidance of a doctor.