Do cough syrups work? Evidence is limited, researchers say

Do cough syrups work for the hacking cough that keeps people awake at night? Researchers Jack Janetzki and Lauren Cortis wrote in The Conversation that the evidence for many over-the-counter cough products is thin, while some basic home measures may provide comparable comfort.

Most coughs, especially those linked to short viral infections, clear without treatment, the researchers said. A cough is a symptom and a protective reflex that helps clear the airways, rather than a disease on its own.

Some coughs still need medical attention. Janetzki and Cortis said any cough lasting more than four weeks should be checked by a primary care doctor, and symptoms such as trouble breathing or swallowing, coughing blood or chest pain should prompt urgent care.

Do cough syrups work?

Cough syrups are usually sold for either dry coughs or productive coughs. Dry-cough products often contain cough suppressants, while products for mucus-producing coughs may include ingredients meant to break up, thin or loosen mucus.

The researchers said there is limited good-quality evidence that cough mixtures improve coughs overall. One exception is dextromethorphan, a cough suppressant with good evidence of effectiveness, though it can cause side effects including nausea and drowsiness and should be used according to the label.

Other ingredients have weaker support. Janetzki and Cortis said there is little evidence that dihydrocodeine, another cough suppressant, works; because it is an opioid and can be misused, it is sold in Australia only under pharmacist supervision. Pholcodine, another suppressant, was removed from Australian pharmacies in 2023 because of safety concerns tied to dangerous immune reactions with muscle relaxants used during general anesthesia.

For productive coughs, the researchers said evidence is also limited for mucus-related ingredients such as bromhexine and guaifenesin. They added that cough medicines are not recommended for children because there is no evidence they work in that group.

What about lozenges and medicated hot drinks?

Lozenges may briefly soothe a sore or irritated throat, according to the researchers, but there is little evidence that they shorten a cough. Some lozenges contain herbal ingredients that may pose risks for people with allergies; andrographis, for example, has been linked to rare serious allergic reactions including anaphylaxis.

Medicated hot drinks often contain acetaminophen, vitamin C and phenylephrine. Janetzki and Cortis said acetaminophen may help if fever or body aches are present, while orally taken phenylephrine has little to no effect as a decongestant.

The researchers said the warm liquid itself may account for much of the relief people feel from these drinks. They also warned people to avoid accidentally taking the same medicine in multiple forms, such as a hot drink plus a tablet or syrup.

What helps a cough at home?

Honey has better evidence than many common cough products, according to Janetzki and Cortis. They cited a 2020 meta-analysis of 14 studies that found honey reduced cough frequency and severity and soothed the throat, performing as well as or better than many cough medicines.

Warm fluids and steam inhalation can also help loosen mucus and moisten the airways, the researchers said. They also noted that staying current on vaccinations can reduce the risk of some illnesses that cause coughs, and that people 65 and older in Australia are eligible for pneumococcal vaccination.

For many short-lived coughs, the practical choice is symptom relief while the body recovers. If the cough persists, worsens or comes with warning signs, the researchers said it should be treated as a reason to seek medical advice rather than another product from the medicine cabinet.

This story draws on original reporting from Medical Xpress.