Theophylline extended-release tablets side effects need to be judged according to the concentration of the drug in the blood, generally the concentration of theophylline in the blood is less than 20 μg/m, the side effects are not big, if the concentration of theophylline in the blood is more than 20 μg/m, the side effects are bigger. Theophylline extended-release tablets belong to smooth muscle relaxants, mainly used in the treatment of bronchial asthma, wheezing bronchitis, obstructive emphysema and other diseases. Whether theophylline extended-release tablets side effects are large, need to be judged according to the concentration of the drug in the blood, if the serum theophylline concentration of 15-20μg/ml, the patient may experience nausea, vomiting, insomnia and other uncomfortable symptoms, the general side effects are not large. In addition, when the serum theophylline concentration exceeds 20 μg/ml, the side effects are greater. Patients may experience symptoms such as tachycardia, arrhythmia and fever. Even in severe cases, the manifestations such as respiratory and cardiac arrest may occur. Therefore, patients need to test the serum theophylline concentration regularly during the medication. For patients taking theophylline extended-release tablets drug, need to standardize the use of medication under the guidance of the doctor, not self-medication, in order to prevent adverse consequences.