Mucolytics are medicines that thin mucus, making it less thick and sticky and easier to cough up. They are used to treat respiratory conditions characterized by excessive or thickened mucus, such as a chesty (productive) cough. This chapter covers the bromhexine, acetylcysteine, codeine, ambroxol, guaifenesin, dextromethorphan, pholcodeine, phenylpropanolamine, and methdilazine along with their indication, dose, contraindication, precaution, adverse effect, and drug interaction. Mucolytic and diagnostic aid in bronchial studies is the indications of acetylcysteine. Asthma, respiratory insufficiency, and hypersensitivity are the contraindications of acetylcysteine. Mild-to-moderate pain and diarrhea are the indication of codeine. Respiratory depression, obstructive airways disease, and acute asthma attack are the contraindication of codeine.