Staff Sgt. Tyler Durden and his fellow soldiers have been at the shooting range since 3 a.m. Every few seconds, a piercing shot from an M16 rifle rings out. With sunrise still an hour away, shell casings litter the ground.

The M16 is one of the U.S. Army’s quieter weapons, but that isn’t saying much. For the shooter, shots from the rifle, even if muffled by Army-issue earplugs, register above the noise level hearing experts consider safe. Over 11 days at the range as the soldiers train to become drill sergeants, each will fire an M16 at least 500 times. The Army is worried about hearing loss.

That is why, when the troops line up for breakfast under a tent, Sgt. Durden steps away to see two civilian nurses waiting at the side, who hand him a small bottle. He downs the liquid in one gulp before hurrying back to the breakfast line.

Sgt. Durden is a participant in a clinical trial, one tackling an issue that is both costly and garnering greater awareness in the military: hearing damage. Such damage traces not just to explosive sounds such as an M16 shot—a momentary 155 decibels, far louder than a jackhammer—but also to constant exposure to lesser noise such as that of engines. The trial is testing an experimental drug that might prevent noise-induced hearing loss, in a collaboration between an academic scientist and the military.

If ultimately endorsed by federal regulators, the drug would be the first approved to prevent hearing loss. It could have benefits far beyond the military. Factory workers, miners, loggers, musicians, pilots and others who work in noisy industries face high rates of hearing damage. Globally, a billion teenagers are putting themselves at risk through the din of clubs, concerts and even some sports events, the World Health Organization estimates.

The compound being tested, a liquid form of a micronutrient called d-methionine that is found in cheese and other foods, was developed into a drug by Kathleen C.M. Campbell, an audiologist and professor at Southern Illinois University School of Medicine.

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