Q. My cold is better, but I can’t stop coughing. Isn’t there a cold medicine that works?

A. The search for an effective cough medicine can be frustrating.

Americans spend $8 billion a year on over-the-counter cough and cold products, yet there is little evidence that they suppress coughs. The American College of Chest Physicians underscored this point bluntly in 2017: “For adult and pediatric patients with cough due to the common cold, we suggest against the use of over-the-counter cough and cold medicines until they have been shown to make cough less severe or resolve sooner.”

When over-the-counter products fail, cough sufferers often look for “something stronger” — namely codeine, widely regarded as the standard by which cough medicines are measured. Much of the interest in codeine dates from a 1950 experiment, unlikely to be undertaken today, in which 17 Swedish medical students agreed to inhale ammonia fumes. The cough that ensued was modestly ameliorated by pretreatment with escalating doses of codeine.

But a subsequent double-blind, placebo-controlled trial of 82 patients with upper respiratory infections found that the drug was “no more effective than placebo,” and some experts have labeled the cough-suppressing effect of codeine a “medical myth.”