Cough drops are frequently used to provide short-term relief from symptoms of an upper-respiratory tract infection -- such as the common cold, the flu or a chest cold. Various brands of cough drops contain different active ingredients intended to temporarily quiet a cough. Cough drops are generally safe and unlikely to cause significant side effects. They can, however, cause harmful side effects on heart rate in rare cases. This occurs almost exclusively when cough drops are used to excess.
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Dextromethorphan is a cough suppressant medication included in some cough drops (Cepacol Sore Throat and Cough, Chloraseptic Sore Throat and Cough, Delsym Cough and Sucrets Cough lozenges). The medication acts in the brain’s cough center, suppressing the signals that trigger a cough. While somewhat effective in temporarily relieving coughing, dextromethorphan can have negative effects on the heart if overused. When taken in excess, dextromethorphan can cause a fast and/or irregular heart rate. These effects are typically seen in combination with other symptoms, including nausea, vomiting, unsteadiness while walking, hallucinations and possibly seizures. Overuse and abuse of dextromethorphan is especially common in the adolescent population because of its hallucinatory effects.
Dyclonine and Benzocaine
Dyclonine and benzocaine are locally acting numbing medications found in some cough drops (Sucrets, Cepacol and Chloraseptic lozenges). These medicines provide temporary relief of throat pain and irritation by mildly numbing the throat, which can help reduce coughing. In very rare cases, benzocaine can lead to an elevated heart rate. This is typically seen along with gray- or blue-colored skin, lips and nail beds, shortness of breath, fatigue, confusion and headaches. Dyclonine is much less likely to cause side effects, as it is poorly absorbed by the body. In either case, symptoms are almost exclusively caused by taking far more medication than directed.
Other ingredients in cough drops may rarely cause side effects. Some cough drops include eucalyptus oil (Halls Mentho-Lyptus and Burt's Bees Natural Throat drops), to temporarily relieve airway inflammation and coughing. Though very rare, a eucalyptus oil overdose can cause nervous system depression and a slow heart rate. This is usually proceeded by burning in the stomach, vomiting, difficulty walking or seizures. Many drops (Halls and Vicks) also contain menthol, which provides a cooling sensation in the airways and a mild numbing effect on the throat. Excessive amounts of menthol can lead to an elevated heart rate, but this is very unlikely to occur with cough drops due to the small amount they contain.
Other cough drops contain zinc gluconate (Cold-eeze), a mineral supplement that might decrease the duration of symptoms associated with the common cold. In large doses, zinc gluconate can cause anemia -- a low level of red blood cells. This can lead to fatigue, weakness, irritability and an elevated heart rate.
Warnings and Precautions
Some ingredients in cough drops can rarely affect heart rate, but changes in heart rate are more likely to be caused by complications of an upper respiratory tract infection. People experiencing an increased or irregular heart rate along with a cough, fever, shortness of breath or chest pain should seek immediate treatment as these symptoms may indicate pneumonia or another serious problem. This is especially true for people with preexisting heart disease or a heart rhythm abnormalities, who are more susceptible. In addition, anyone with a cough that lasts longer than 7 days or that is accompanied by bloody phlegm, unexplained weight loss or fevers with night sweats should seek medical attention as soon as possible.