Tinnitus can feel like a cruel trick of the brain. It's a persistent ringing or buzzing in your ears when no external source is present. For some, tinnitus is a mild annoyance. For others, it's a constant intrusion linked to anxiety, sleep disruption and even depression.

New research offers a deeper understanding of why this condition may worsen in some patients, particularly those taking medications that affect serotonin, a chemical that carries messages between our nerve cells.

The study was led by researchers at Anhui University in China and Oregon Health & Science University (OHSU).

Serotonin can increase the excitability of neurons in auditory regions, effectively “turning up the volume” on internal noise.

Their findings center on serotonin, a neurotransmitter widely known for its role in regulating mood and the primary target of commonly prescribed antidepressants known as selective serotonin reuptake inhibitors (SSRIs). These drugs work by increasing serotonin levels in the brain, often with life-changing benefits for people with depression and anxiety.

This study suggests a more complicated picture, however.

Using a mouse-model, researchers identified a specific brain circuit linking serotonin-producing neurons in the dorsal raphe nucleus to the auditory system, specifically, the dorsal cochlear nucleus.

When this serotonergic pathway was activated, the animals began to behave as though they were hearing phantom sounds, a hallmark of tinnitus.

“When you stimulate these serotonergic neurons, we can see that it stimulates activity in the auditory region in the brain,” corresponding author Laurence O. Trussell, PhD., a professor of otolaryngology at OHSU School of Medicine and a scientist at the OHSU Vollum Institute and Oregon Hearing Research Center, explained in a press release. “We also saw that animals then behaved as if they were hearing tinnitus.” In other words, boosting serotonin didn't just affect a mood-related circuit, it directly influenced how the brain processed sound.

Even more intriguing, when researchers “turned off” this specific circuit, the tinnitus-like behaviors significantly decreased. This reversibility points to a potential future target for treatment, one that could preserve serotonin's mental health benefits, while minimizing its effect on hearing.

The implications are significant. Tinnitus affects an estimated 14 percent of the global population, and many patients also struggle with anxiety or depression, conditions often treated with SSRIs. For some, these medications may inadvertently worsen the very auditory symptoms that contribute to emotional distress.

Still, experts caution against drawing an overly simple conclusion. This was an animal study, and the human brain is far more complex. Not everyone who takes an SSRI develops tinnitus, and not everyone with tinnitus is affected by serotonin in the same way. What the research does underscore is the importance of individualized care.

“People with tinnitus should work with their prescribing physician to find a drug treatment that gives them balance,” Trussell said, emphasizing the need to weigh mental health benefits against the potential auditory side effects.

Not everyone who takes an SSRI develops tinnitus, and not everyone with tinnitus is affected by serotonin in the same way.

The study also builds on earlier work suggesting that serotonin can increase the excitability of neurons in auditory regions, effectively “turning up the volume” on internal noise. Now for the first time, researchers have mapped a direct circuit that helps explain how that happens.

Looking ahead, the goal is not to abandon serotonin-based treatments, but to refine them. Scientists hope to develop more targeted therapies, ones that can boost mood without overstimulating the auditory system.

For patients, the takeaway is both cautionary and hopeful. If tinnitus worsens after starting a medication, it's worth discussing with a healthcare provider. Adjustment in dosage, timing or drug class may help.

At the same time, this research brings validation. For years, some patients have reported that their tinnitus flared after starting antidepressants. Now, science is beginning to understand why.

The study is published in PNAS.