A new study suggests that fluoxetine, commonly known as Prozac, may do more than treat depression. Researchers at the Salk Institute found that it could also protect against serious infections and even deadly conditions like sepsis.
These discoveries could lead to new treatments and help prepare for future pandemics. The study was published in Science Advances on February 14, 2025.
How Fluoxetine Protects Against Infections
Fluoxetine belongs to a group of medications called selective serotonin reuptake inhibitors (SSRIs), which are widely used to treat depression and anxiety.
However, researchers noticed that people taking SSRIs had milder COVID-19 infections and were less likely to develop long-term complications. This raised an interesting question: Could fluoxetine help the body fight infections?
Another study had already shown that fluoxetine could protect mice from sepsis, a life-threatening condition where the immune system overreacts to an infection. Sepsis can lead to organ failure and death. The new research from Salk aimed to understand exactly how fluoxetine provides this protection.
Testing Fluoxetine in Mice
To study the effects of fluoxetine, scientists at Salk infected two groups of mice with bacteria. One group was given fluoxetine before the infection, while the other group was not. The results were striking—mice that received fluoxetine were far less likely to develop sepsis or suffer organ damage.
Researchers then performed more tests to understand why fluoxetine had this protective effect.
Fighting the Infection – The team measured bacteria levels in both groups of mice eight hours after infection. The mice treated with fluoxetine had fewer bacteria, meaning their infections were less severe. This suggested that fluoxetine has antibacterial properties that help control infections.
Preventing Organ Damage – The researchers also checked for signs of inflammation, which can cause serious harm in conditions like sepsis and severe COVID-19. They found that fluoxetine increased levels of a molecule called IL-10, which reduces inflammation. IL-10 helped prevent a dangerous condition known as hypertriglyceridemia, where too much fat builds up in the blood, damaging the heart and other organs.
Independent of Serotonin – Since fluoxetine is best known for increasing serotonin, which affects mood and emotions, scientists wondered if serotonin played a role in its infection-fighting ability.
To test this, they studied another set of mice—both treated with fluoxetine, but one group had normal serotonin levels while the other had none. Surprisingly, both groups showed the same level of protection. This proved that fluoxetine’s ability to fight infections was separate from its role in treating depression.
Why This Discovery Matters
Most infection treatments focus on killing bacteria or viruses, but fluoxetine appears to work in two ways—it fights infections while also protecting the body from harmful immune overreactions. This dual action makes it an exciting candidate for future treatments, especially for conditions like sepsis, where inflammation causes as much damage as the infection itself.
Professor Janelle Ayres, who led the study, says that most medications either attack the infection or control inflammation. Fluoxetine does both, which could make it a valuable tool for doctors. Since fluoxetine is already widely used and considered safe, it could be tested for infection treatment sooner than brand-new drugs.
What’s Next?
The researchers plan to study fluoxetine further to determine the right dosage for treating infections in humans. They also want to test whether other SSRIs have the same effects. If successful, this could lead to a new way to treat infections and reduce deaths from conditions like sepsis.
Study author Robert Gallant describes these findings as a major step forward. “Knowing fluoxetine can fight infections and protect organs, completely separate from serotonin, is a huge discovery,” he says. “It shows how much we still have to learn about these drugs.”
Professor Ayres adds that finding such powerful effects in a drug that’s already approved is rare. “Fluoxetine is one of the most commonly prescribed medications in the U.S. If it can also help fight infections, it could save countless lives.”
This research opens up new possibilities for using antidepressants in unexpected ways. If further studies confirm these benefits, fluoxetine might not just be a mental health drug—it could also become a life-saving treatment for infections and immune-related illnesses.
If you care about mental health, please read studies about how dairy foods may influence depression risk, and 6 foods you can eat to improve mental health.
For more mental health information, please see recent studies about top foods to tame your stress, and Omega-3 fats may help reduce depression.
The research findings can be found in Science Advances.
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