By Sola Ogundipe

A groundbreaking study has suggested that a common type of antidepressant could help the body fight off cancer by shrinking tumours by more than 50 percent. 

The research, published in the journal *Cell*, focused on selective serotonin reuptake inhibitors (SSRIs), a medication widely used to treat mood disorders. While SSRIs are typically associated with altering serotonin levels—the neurotransmitter known as the brain’s “happiness hormone”—scientists sought to determine whether they also influence other bodily processes, particularly those involved in preventing tumor growth. 

Researchers at the University of California discovered that certain tumor cells contain high levels of molecules that break down serotonin. To counteract this, they investigated whether SSRIs, which block serotonin degradation, could enhance the body’s natural ability to combat cancer. 

Their tests on mice with cancerous tumors, as well as human cancer cells in laboratory settings, showed promising results. The antidepressant treatment appeared to reinvigorate T cells, which are responsible for fighting diseases, making them more effective at killing cancer cells. 

Senior study author Dr. Lili Yang explained, “It turns out SSRIs don’t just make our brains happier, they also make our T cells happier. SSRIs increase T cells’ access to serotonin signals, reinvigorating them to fight and kill cancer.”

Beyond shrinking tumors, SSRIs also boosted the effectiveness of existing cancer therapies. When combined with anti-PD-1 antibody treatment—a therapy that removes immune system suppression—researchers saw a significant reduction in tumor size and even complete remission in some cases. 

Despite the promising findings, scientists caution that the results are based on lab experiments and animal testing, not human trials. To further assess SSRIs’ potential as a cancer treatment, researchers plan to examine real-world data from cancer patients who coincidentally take antidepressants. 

Currently, millions worldwide take SSRIs for depression and anxiety, with the UK reporting over 8.7 million prescriptions in England alone. In the U.S., approximately one in eight people are prescribed an antidepressant, according to the Centers for Disease Control and Prevention. 

While SSRIs may present a new avenue for cancer treatment, experts note the drug has been linked to long-term health effects, including persistent sexual dysfunction. Researchers hope that further investigation will clarify the benefits and risks before SSRIs can be repurposed for broader clinical use.