Pilot trial suggests anti-inflammatory drug could help difficult-to-treat depression
Photo Credit: Anna Shvets
Scientific Frontline: Extended "At a Glance" Summary: Immunotherapy for Difficult-to-Treat Depression
The Core Concept: A recent pilot clinical trial indicates that tocilizumab, an existing anti-inflammatory drug, shows promise in alleviating symptoms for patients with difficult-to-treat depression. By treating depression as an immune-related condition rather than solely a neurochemical one, this approach offers a new therapeutic avenue for those unresponsive to standard medications.
Key Distinction/Mechanism: Unlike traditional antidepressants that target brain chemicals like serotonin and dopamine, this treatment blocks the interleukin-6 (IL-6) inflammatory pathway. This mechanism specifically targets the estimated one-in-three depressed patients who exhibit signs of an overactive immune system and low-grade inflammation in their blood.
Origin/History: The University of Bristol-led pilot randomized controlled trial was published in JAMA Psychiatry on May 20, 2026. The trial was built upon foundational genetic research utilizing Mendelian randomization, which previously established a causal link between the IL-6 cytokine and depression.
Major Frameworks/Components:
- Interleukin-6 (IL-6) Pathway: A specific cytokine and inflammatory protein targeted by the drug to reduce body-wide inflammation linked to depressive symptoms.
- Mendelian Randomization: The genetic analytical technique used in prior studies to separate correlation from causation, proving the initial theory that inflammation actively contributes to depression.
- Tocilizumab Repurposing: The utilization of an established rheumatoid arthritis drug for targeted psychiatric treatment.
- Precision Patient Selection: The trial required participants to demonstrate low-grade inflammation in multiple blood tests before treatment, establishing a framework for biology-based tailored care.
Branch of Science: Immunopsychiatry, Psychiatry, Immunology, and Pharmacology.
Future Application: The promising preliminary results will pave the way for a large-scale phase III randomized control trial. If definitive evidence is gathered, doctors will be able to prescribe targeted immunotherapy, moving the field toward highly personalized psychiatric care.
Why It Matters: With traditional antidepressants failing approximately one-third of all patients, this novel approach provides a vital alternative. The trial demonstrated a depression remission rate of 54% in the treatment group compared to 31% in the placebo group, showing a potentially higher efficacy for inflamed patients than standard first-line SSRIs.
Immunotherapy could be a promising new treatment option for patients with difficult-to-treat depression. This is a key finding from a University of Bristol-led pilot randomized controlled clinical trial published in JAMA Psychiatry.
Researchers investigated, for the first time, whether tocilizumab, an existing anti-inflammatory drug commonly used to treat immune conditions such as rheumatoid arthritis, could improve symptoms of depression in people who have not responded to standard antidepressant treatments.
While the pilot trial involved a small number of people (thirty participants with moderate-to-severe depression), it provides early evidence that, compared with a saltwater placebo, tocilizumab may reduce depression symptoms, fatigue, and anxiety, as well as increase overall quality of life.
Current drug treatments for depression are solely based on targeting chemicals in the brain, such as serotonin, norepinephrine, and dopamine. However, around one in three people with depression do not get better with these treatments.
Recent research shows that about one in three people with depression have signs of inflammation in their blood, indicating that, for some, their symptoms may be linked to an overactive immune system. Other studies point to higher levels of certain inflammatory proteins, called cytokines, in depression, including interleukin 6 (IL-6), a cytokine that plays a key role in the body’s inflammatory response.
Earlier work by the team using Mendelian randomization further supports the idea that inflammation, particularly the cytokine IL-6, may contribute to depression. This genetic technique allows researchers to identify causal factors for disease by teasing apart correlation from causation, making use of the underlying genetic differences within large populations. Studies using Mendelian randomization, along with other study designs like longitudinal cohort studies, together provide triangulated evidence all pointing toward the IL-6 inflammation pathway as one of the key causes of depression.
Researchers wanted to see whether symptoms could improve in people with inflammation-related depression by blocking the IL-6 pathway, thus lowering inflammation levels. To test this, they conducted a small, four-week pilot randomized controlled trial of thirty people with moderate-to-severe depression who had not responded well to standard antidepressants and who showed signs of low-grade inflammation in two separate blood tests taken two weeks apart. Participants were randomly assigned to receive either tocilizumab (fourteen people) or a placebo (sixteen people) and were followed over four weeks to record any effects.
While the results showed little statistical evidence for a significant difference between the two groups, as expected for a small study, participants who received tocilizumab seemed to experience greater improvements over time across several measures compared to those given a placebo, including overall depression severity, fatigue, state anxiety, and quality of life. Furthermore, the tocilizumab group was more likely to achieve depression remission compared to the placebo group (54% vs. 31%), which equates to a number needed to treat (NNT) of five, meaning an additional five patients will need to be treated to make one patient better. For comparison, the NNT for SSRIs—the most common first-line antidepressant for patients with moderate-to-severe depression—is about seven.
Golam Khandakar, professor of psychiatry and immunology from the MRC Integrative Epidemiology Unit (MRC IEU) at the University of Bristol and the NIHR Biomedical Research Centre: Bristol (NIHR BRC: Bristol), and the study’s senior author and chief investigator, said, “This work represents 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. This is one of the first randomized controlled trials to test immunotherapy for depression, the first to test IL-6R as the treatment target, and the first to use a targeted approach to select patients most likely to benefit, and to show that it works.”
Dr. Éimear Foley, senior research associate in immunopsychiatry at Bristol's MRC IEU and the NIHR BRC: Bristol, and the study's lead author, added, “Depression is estimated to affect around 10%–20% of people worldwide during their lifetime, yet for many patients, current treatments do not work well enough. Our study moves us closer to more tailored depression care, where treatments are chosen to better fit a person’s biology. This will help us to provide the right treatment to the right patients at the right time.”
One participant who took part in this study said, "I was happy to take part. Without research, advancements in medicine cannot be made."
The next step will be to conduct a large-scale phase III randomized controlled trial that will provide definitive evidence to enable doctors to prescribe immunotherapy for depression.
Funding: The research was funded by Wellcome. The research received additional funding from the NIHR BRC: Bristol, NIHR BRC: Cambridge, and a BMA Foundation J Moulton grant.
Published in journal: JAMA Psychiatry
Title: Interleukin 6 as a Treatment Target for Depression
Authors: Éimear M. Foley, Nicholas Turner, Ruta Margelyte, Hannah J. Jones, Muzaffer Kaser, Glyn Lewis, Peter B. Jones, and Golam M. Khandaker
Source/Credit: University of Bristol
Edited by: Scientific Frontline
Reference Number: psyc052026_01
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