Recent clinical trials suggest that treating the immune system with anti-inflammatory drugs may reduce symptoms in patients with hard-to-treat depression. This study provides early evidence that lowering inflammation levels tends to improve mood, fatigue, and anxiety in these people. Research results were published in a medical journal JAMA Psychiatry.
Standard medical treatment for depression usually focuses on brain chemistry. These drugs are designed to change the levels of neurotransmitters such as serotonin and dopamine. Although these drugs help many people, about 1 in 3 people with depression do not experience sufficient relief from them.
Scientists suspect that other biological systems may be responsible for mood disorders in some patients. Recent studies have shown that about one-third of people with depression have persistent signs of inflammation in their blood. This suggests that their symptoms may be related to an overactive immune system, not just a chemical imbalance in the brain.
Inflammation is a natural response the body uses to heal injuries and fight infections. In some cases, the immune system can remain at a low level for an extended period of time. This mild systemic inflammatory condition affects the brain and can change a person’s behavior and mood.
During an immune response, the body produces proteins called cytokines. Cytokines act as chemical messengers that signal the immune system to take action. Previous observational studies have consistently linked high levels of a particular cytokine called interleukin-6 to depression.
Previous studies by the research team used a genetic method called Mendelian randomization. This method examines natural genetic variation in large populations to help scientists distinguish underlying correlations from true biological causes. These genetic studies provided strong evidence that the interleukin-6 pathway is a causative factor in depression, prompting the research team to conduct a clinical trial.
Lead author Eimear M. Foley, a researcher at the University of Bristol, and his colleagues wanted to test this connection in a real-world setting. They designed a study to see if blocking the interleukin-6 biological pathway could reduce symptoms of depression. To accomplish this, they utilized an existing arthritis drug called tocilizumab.
Tocilizumab is an immunotherapy drug that blocks interleukin-6 receptors in the body. This drug reduces the overall inflammatory response by blocking these receptors. The researchers aimed to determine whether giving the drug to depressed patients with high levels of inflammation would result in significant improvements.
Scientists designed a four-week randomized, placebo-controlled trial. They recruited 30 adults who were currently suffering from moderate to severe depression. All participants had a history of trying standard antidepressants without obtaining adequate relief.
To ensure they were testing the right population, researchers asked participants to show signs of persistent, low-grade inflammation. They measured a specific substance in the blood called high-sensitivity C-reactive protein. This protein is produced by the liver and serves as a reliable marker of overall inflammation in the body.
Participants were required to undergo two separate blood tests two weeks apart. Both tests needed to show elevated levels of C-reactive protein. This requirement helped scientists confirm that inflammation is a chronic problem, not just a temporary response to a cold or minor infection.
Researchers randomly divided 30 participants into two groups. 14 received a single intravenous infusion of tocilizumab. Dosage was calculated based on each patient’s specific body weight.
The remaining 16 participants received one intravenous infusion of a simple saline placebo. The study was double-blind, meaning neither patients nor researchers knew who received the actual drug until the end of the trial. This design helps prevent expectations from influencing the recorded results.
After the injection, the scientists followed the participants for 28 days. They conducted detailed assessments at 1 week, 2 weeks, and 4 weeks. During these check-ins, participants completed validated questionnaires to assess physical and psychological symptoms.
The researchers were particularly interested in the physical symptoms of depression. Somatic symptoms are the physical manifestations of the disorder, such as deep fatigue, changes in appetite, and sleep disturbances. They also tracked overall depression severity, anxiety, and general quality of life.
Because this was a small proof-of-concept study, the researchers did not expect the results to reach statistical significance. Statistical significance is a mathematical criterion used to confidently eliminate chance in scientific data. Although the results did not meet this strict threshold, the data showed a consistent pattern of improvement favoring the medication.
Participants who received tocilizumab experienced gradual symptom relief. This means that a patient’s condition tends to improve gradually over time, with the most noticeable effects occurring during the last 28 days of evaluation. The group receiving the drug reported steady reductions in both physical symptoms and overall depression severity.
The researchers also observed improvements in individual symptoms. The tocilizumab group reported less fatigue, improved concentration, and improved appetite. They also reported less feelings of worthlessness and physical arousal compared to the placebo group.
At the end of the four-week period, approximately 54 percent of participants in the medication group achieved remission of depression. Remission means that symptoms have reduced to the point where they are no longer considered clinically depressed. In the placebo group, approximately 31% of participants achieved remission.
The researchers calculated that five patients would need to receive the drug, with one more person receiving it, to achieve remission. This indicator helps physicians understand the practical benefits of drugs in clinical practice. For context, common antidepressants typically require treating about seven people to see one additional positive result.
The study also revealed a relationship between initial inflammation levels and treatment success. Participants who had higher levels of C-reactive protein at the start of the study tended to show the greatest improvement after receiving tocilizumab. Interestingly, initial levels of interleukin-6 did not predict treatment response as accurately as C-reactive protein levels.
This finding provides evidence that a simple blood test for C-reactive protein may help doctors identify suitable candidates for immunotherapy. This procedure was well accepted by participants. No serious adverse events or medical complications were reported during the trial.
The authors note that this study has several limitations. The small sample size means that a positive trend cannot conclusively prove the drug’s effectiveness. The 4-week follow-up period was also relatively short, so it is unclear whether the effects last for months or years.
The participant group lacked significant demographic diversity, limiting the extent to which the findings could be applied to the broader population. Researchers emphasize the need for larger clinical trials with more diverse participants. These future studies may test treatments over longer periods of time and use repeated doses of the drug.
Current psychiatric care often relies on a trial-and-error approach when prescribing antidepressants. Patients may try several drugs before finding one that works. The approach tested in this study is oriented toward precision medicine, a strategy in which treatments are specifically selected to suit an individual’s unique biological makeup.
Despite its limitations, this trial represents an important step forward in psychiatric research. The findings suggest that targeting a patient’s specific immune profile may open new avenues. Such an individualized approach may ultimately bring relief to individuals who have been battling treatment-resistant depression for years.
The study, “Interleukin-6 as a therapeutic target for depression: A proof-of-concept randomized clinical trial,” was authored by Éimear M. Foley, Nicholas Turner, Ruta Margelyte, Hannah J. Jones, Muzaffer Kaser, Glyn Lewis, Peter B. Jones, and Golam M. Khandaker.
