Researchers at the University of Bristol have made a striking discovery: tocilizumab, a drug long used to treat rheumatoid arthritis, may ease depression in patients for whom every standard antidepressant has failed. In a randomized controlled trial published in JAMA Psychiatry on May 20, scientists tested whether an anti-inflammatory approach could work where conventional brain-focused treatments could not — and the early results suggest a fundamentally new path forward for millions struggling with treatment-resistant depression.
The reason this matters is simple: roughly one-third of people with depression do not respond adequately to traditional antidepressants, which work by increasing levels of brain chemicals like serotonin, dopamine, and norepinephrine. For those patients, the options have been limited. Now researchers are asking whether depression in some cases might not be a chemical imbalance in the brain at all, but rather a problem of inflammation in the immune system.
Recent science has shown that about one in three people with depression have elevated inflammatory markers in their blood, pointing to a possible immune system involvement in their symptoms. In particular, scientists have focused on interleukin 6 (IL-6), a protein that helps regulate the body's immune response, with previous studies linking higher IL-6 levels to depression. The University of Bristol team used Mendelian randomization — a genetic research method that helps separate cause from coincidence — to explore whether inflammation involving the IL-6 pathway might actually be a biological driver of depression for some patients.
To test this hypothesis, researchers recruited 30 people with treatment-resistant depression who also showed signs of low-grade inflammation in blood tests, working through the University of Cambridge and the Cambridgeshire and Peterborough NHS Foundation Trust. Fourteen participants received tocilizumab; sixteen received a saltwater placebo. Over four weeks, researchers monitored changes in depression severity, anxiety, fatigue, and quality of life. Though the trial was small, the findings were striking: 54% of participants taking tocilizumab achieved depression remission, compared to just 31% in the placebo group. The Number Needed to Treat — how many people must receive the drug for one additional person to benefit — was calculated at five. For context, SSRIs, the most commonly prescribed antidepressants for moderate-to-severe depression, have a Number Needed to Treat of around seven.
Professor Golam Khandakar, the study's senior author and chief investigator at the University of Bristol's MRC Integrative Epidemiology Unit, called the work "an important milestone in the development of new treatments for depression especially difficult-to-treat depression, which affects millions of people in the UK alone." Dr. Éimear Foley, the study's lead author, emphasized the shift toward personalized care: "Our study moves us closer to more tailored depression care, where treatments are chosen to better fit a person's biology."
Still, researchers caution that larger studies are essential before immunotherapy could become standard treatment. A phase III randomized controlled trial is already being planned to determine whether doctors should begin prescribing this approach more broadly. For now, the work funded by Wellcome and supported by the UK's National Institute for Health and Care Research represents a crucial next chapter in understanding depression itself — one where immune biology, not just brain chemistry, holds the key to relief.