Interleukin 6 as a Treatment Target for Depression: A Proof-of-Concept Randomized Clinical Trial, Foley et al., 2026

[InitialConditions]

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Interleukin 6 as a Treatment Target for Depression
Visual Abstract.

Importance Interleukin 6 (IL-6), a keystone inflammatory cytokine, is a credible mechanistic candidate for causing depression. However, randomized clinical trials testing its treatment potential remain scarce.

Objective To identify likely treatment-sensitive outcomes and effect size for systemic IL-6 inhibition in patients with difficult-to-treat depression.

Design, Setting, and Participants This 4-week, proof-of-concept, double-blind, parallel-arm, placebo-controlled randomized clinical trial recruited adults with moderate-to-severe International Statistical Classification of Diseases and Related Health Problems, Tenth Revision (ICD-10) depression, poor antidepressant response, low-grade systemic inflammation (high-sensitivity C-reactive protein [hs-CRP] level ≥0.3 mg/dL on 2 tests), and depression somatic symptoms (Beck Depression Inventory II somatic symptoms score ≥7) from primary and secondary care and self-referral from 2018 to 2022. Participants were randomized into minimization balanced groups on depression severity and sex. Assessments were conducted at baseline and 7, 14, and 28 days after infusion. Data were analyzed from 2023 to 2025.

Intervention Single intravenous infusion of IL-6R antagonist tocilizumab (8 mg/kg, maximum 800 mg/patient) or normal saline.

Main Outcomes and Measures The primary outcome was depression somatic symptoms at 14 days after infusion. The secondary outcome was total depression severity. Exploratory outcomes included fatigue, anxiety, anhedonia, quality of life, and cognition. Outcomes were assessed using validated scales and interpreted against clinically meaningful thresholds.

Results A total of 30 participants (mean [SD] age, 41.1 [12.3] years; 24 [80.0%] female) were randomized, including 14 in the tocilizumab group and 16 in the placebo group. Of these, 29 participants received the assigned infusion and completed follow-up. As expected for a small proof-of-concept study, no results reached statistical significance, including little improvement in depression somatic symptoms at day 14 (adjusted mean difference: −0.12; 95% CI, −2.51 to 2.28). However, a pattern of greater stepwise improvement over time was observed with tocilizumab in somatic symptoms, depression severity, fatigue, psychological symptoms, state anxiety, and quality of life, with the largest effects observed at the final follow-up (day 28). Tocilizumab may also improve more individual depressive symptoms. Treatment effects were within ranges considered clinically meaningful for depression severity, fatigue, anxiety, and quality of life. At the final follow-up, remission (7 participants [53.9%] vs 5 participants [31.3%]; number needed to treat [NNT] = 5) and response (6 participants [46.2%] vs 3 participants [18.8%]; NNT = 4) rates favored tocilizumab compared with placebo. Baseline hs-CRP level, but not IL-6 level, tracked depression improvement, suggesting hs-CRP may better predict immunotherapy response in depression than drug-specific biomarkers. Tocilizumab was well tolerated, with no serious adverse events or withdrawals.

Conclusions and Relevance These findings highlight treatment-sensitive outcomes, effect sizes, and patient selection methods for testing systemic IL-6 inhibition in patients with difficult-to-treat depression, and call for a large-scale efficacy trial of anti–IL-6 treatment in depression.

Trial Registration isrctn.org Identifier: ISRCTN16942542

 

[Utsikt]

The claim blinding was successful, but don’t provide any data on it.

Blinding was successful (eAppendix in Supplement 2)

This is all the supplementary file says:

Blinding success was assessed by asking participants and staff to guess allocation at exit.

The protocol also says that they were planning on recruiting 50 participants, not 30. This deviation isn’t mentioned at all in the paper, but is briefly discussed in the supplementary material:

Recruitment was affected by the COVID-19 pandemic, and the study was closed with a final N=30 sample. As a small proof-of-concept trial, the study was not powered for definitive efficacy conclusions. The primary focus was on the overall pattern of results, rather than individual statistical significance tests, with interpretation based on effect size magnitude, confidence intervals, and pattern of change over time relative to clinically meaningful thresholds, when available.

 

[Jonathan Edwards]

As expected for a small proof-of-concept study, no results reached statistical significance, including little improvement in depression somatic symptoms at day 14 (adjusted mean difference: −0.12; 95% CI, −2.51 to 2.28).

If there is no statistical result it is not proof of concept.
I think a decent benefit from Tocilizumab should have been statistically significant even with these numbers. The drug has major potential hazards like infection. When biologics work they usually show it very easily.

 

[BrightCandle]

Its a null result, no clinical significance. It doesn't work there is zero value in pursing this further. Sure has been all over the press that this will help people with depression that resists existing treatment even though their results show nothing of the sort.