This surprising discovery may hold the key to calmer nerves.

A new study out of Brazil found that a low dose of a common antibiotic, typically used to treat acne, rosacea and a range of bacterial infections, could also help people living with panic disorder.

The findings suggest the drug might one day offer an alternative for patients who don’t respond to psychiatric medications, including benzodiazepines, or “benzos,” like clonazepam.

These episodes come on suddenly as waves of intense fear, often striking in otherwise normal, nonthreatening situations. They can bring on physical symptoms such as a racing heart, chest pain, sweating and shortness of breath.

About 11% of Americans experience a panic attack each year. For some, however, these episodes become a regular, unpredictable occurrence — a condition known as panic disorder.

The condition is marked by repeated attacks that seem to come out of nowhere. Roughly 2% to 3% of people in the US live with panic disorder, and women are about twice as likely to be affected as men, according to the Cleveland Clinic.

In the new study, backed by the São Paulo Research Foundation, scientists looked at minocycline, a common antibiotic known for its strong anti-inflammatory effects.

“It’s well known that some psychiatric conditions result from nerve cell inflammation,” Luciane Gargaglioni, one of the study’s authors, said in a press release.

That includes panic disorder, where patients often show increased inflammation in the brain’s immune cells, known as the microglia.

To see whether minocycline could make a difference, researchers first tested it in animals. In the experiment, the team gave mice the antibiotic and, 14 days later, exposed them to air enriched with CO₂, which triggers a suffocation-like sensation similar to a panic attack.

The animals showed noticeable behavioral changes after treatment, including reduced jumping.

A closer look at their brains showed that they also had redcued activity in a region known as the locus coeruleus, which is highly sensitive to carbon dioxide and plays a key role in panic responses.

“We tested different intervals during which changes in the brain could be observed and concluded that six hours after 15 minutes of CO₂ exposure is ideal, which is an important finding for future studies,” said Beatriz de Oliveira, the study’s first author.

The researchers then moved to human testing, recruiting 49 patients diagnosed with panic disorder.

The participants were split into two groups: one receiving clonazepam and the other a lower dose of minocycline than is typically used to treat bacterial infections.

At the start of the study and again after seven days of treatment, participants inhaled air containing carbon dioxide. Researchers then tracked their anxiety symptoms at both points.

They found that participants who took minocycline showed a drop in pro-inflammatory markers in the body, including interleukin (IL)-2sRα and IL-6, along with an increase in IL-10, which helps calm inflammation.

Levels of TNFα — another inflammation-linked molecule — also fell.

“Since minocycline has an anti-inflammatory effect at low doses but not necessarily an antibiotic effect, the improvement in symptoms likely occurs through the reduction of inflammation,” Gargaglioni explained.

“It’s a different mechanism than that used by clonazepam, which acts by inhibiting specific receptors in the brain.”

That difference could be important, because benzodiazepines come with some serious downsides.

The class of medications carries the FDA’s strictest “black box” warning, flagging risks of abuse, addiction, overdose and even life-threatening withdrawal. They can be especially dangerous when combined with opioids, potentially leading to severe drowsiness, slowed breathing, coma or death.

And while they work for many, studies suggest up to half of patients with treatment-resistant anxiety disorders don’t respond to benzos like clonazepam.

Minocycline, on the other hand, has been used in humans for more than 50 years and is generally considered safe.

Common side effects include dizziness, nausea and vertigo. Rare but more serious issues can include tinnitus, autoimmune reactions and changes in pigmentation affecting the skin, nails or teeth with long-term use.

Notably, the doses used in the study were lower than those typically prescribed for infections — which could reduce the risk of side effects and limit concerns about antibiotic resistance.

Still, experts caution it’s too early to start prescribing minocycline for panic disorder.

However, because the drug is already widely used for other conditions, the researchers said it could move more quickly into larger clinical trials. That could bring scientists one step closer to confirming whether the antibiotic could help calm panic at its source.

The findings may also open the door to a new wave of treatments targeting brain inflammation, which could prove even more effective in tackling panic disorder in the future.