Researchers have reported promising early results from a new approach to treating depression that focuses on the immune system rather than brain chemistry.

A pilot clinical trial led by the University of Bristol found that tocilizumab — an anti-inflammatory drug commonly used to treat rheumatoid arthritis — may help reduce symptoms in people with treatment-resistant depression.

The findings, published in JAMA Psychiatry on May 20, suggest the medication could lessen depression severity, anxiety, and fatigue while also improving patients’ quality of life.

Most antidepressants currently target neurotransmitters such as serotonin and dopamine. However, nearly one-third of patients do not respond adequately to standard medications, prompting scientists to explore other biological mechanisms linked to depression.

Growing evidence suggests inflammation may play a role in some cases of the disorder. Previous studies have shown that around one in three people with depression have elevated levels of inflammatory markers in their blood.

Researchers have focused particularly on interleukin-6 (IL-6), a protein involved in immune responses that has been associated with depression in earlier studies.

To investigate whether blocking IL-6 could improve symptoms, scientists conducted a four-week randomized controlled trial involving 30 people with moderate-to-severe treatment-resistant depression and signs of low-grade inflammation.

Fourteen participants received tocilizumab, while sixteen were given a placebo. Although the study was small and the statistical evidence remained limited, patients treated with the anti-inflammatory drug generally showed greater improvement over time.

According to the researchers, 54% of participants receiving tocilizumab achieved remission from depression, compared with 31% in the placebo group. The treatment also appeared to improve fatigue, anxiety, and overall well-being.

Professor Golam Khandakar, the study’s senior author from the University of Bristol, described the research as an important step toward developing new therapies for people with difficult-to-treat depression.

Lead author Dr. Éimear Foley said the findings could pave the way for more personalized mental health care, with treatments tailored to an individual’s biology rather than relying on a one-size-fits-all approach.

Researchers stressed that larger studies are still needed before immunotherapy can become a standard treatment for depression. A large phase III clinical trial is expected to be the next stage of research.