You can take amoxicillin for an old cough, but it does not always work because amoxicillin is an antibiotic and is only effective for coughs caused by bacterial infections. It is not effective for viral infections and coughs caused by atypical pathogens such as mycoplasma. You need to determine the cause of the old cough according to the examination results, exclude bronchitis, pneumonia, cough variant asthma and other diseases, improve the blood routine, chest CT, antibodies to Mycoplasma pneumoniae and other tests, and if necessary, improve the bronchial excitation test and lung function test.