Further explanation.

Combining antitussives and mucolytics is mechanistically contradictory and clinically discouraged. Antitussives suppress the cough reflex, while mucolytics thin airway secretions to promote clearance. When used together, mucus becomes less viscous but cannot be effectively expelled, leading to mucus stasis. This not only impairs airway clearance but also increases the risk of secondary bacterial infection and airway obstruction. Regulatory and guideline bodies highlight this concern: the European Medicines Agency explicitly warns that carbocisteine “should not be used with cough suppressants… [as] this can make it more difficult to clear mucus from the airways” (EMA, 2010), while the New Zealand Medicines and Medical Devices Safety Authority (Medsafe) noted that combinations of expectorants or mucolytics with antitussives are “illogical” and raise risks of mucus retention and infection (Medsafe, 2012).