Why Some Depression Resists Treatment — And What Helps

When Standard Antidepressants Simply Don't Work

For roughly one in three people diagnosed with major depressive disorder, first-line antidepressants — SSRIs, SNRIs, and related medications — provide little to no meaningful relief. This is the clinical reality of treatment-resistant depression (TRD), and according to a new expert analysis published in Psychiatric Times (March 2026), the reasons it happens are far more complex than a single broken serotonin pathway.

The piece brings together leading psychiatrists to explain how brain circuitry dysfunction, systemic inflammation, hormonal dysregulation, and unaddressed comorbid conditions all interact to make standard antidepressants miss the mark entirely for a substantial portion of patients. Understanding why depression resists treatment is increasingly essential — both for clinicians designing treatment plans and for patients who have spent years cycling through medications without success.

The Hidden Factors Behind Treatment Resistance

The Psychiatric Times analysis highlights several overlapping mechanisms that drive TRD:

• Brain circuitry disruption: TRD is increasingly understood as a disorder of neural circuit function — particularly in the prefrontal cortex and limbic system — rather than purely a neurotransmitter deficit. Serotonin-targeting drugs don't directly repair dysfunctional circuits, which may explain their limited efficacy in this population.
• Chronic inflammation: Elevated inflammatory markers (such as C-reactive protein and interleukin-6) are found in a meaningful subset of depressed patients who don't respond to conventional antidepressants. Inflammation can disrupt neuroplasticity and blunt the brain's ability to form new, healthy neural connections — a process critical to mood recovery.
• Hormonal imbalances: Dysregulation of the HPA (hypothalamic-pituitary-adrenal) axis, including cortisol abnormalities, contributes to both the onset and persistence of depression. Hormonal factors are frequently overlooked in standard psychiatric workups despite their documented role in treatment response.
• Undiagnosed or undertreated comorbidities: Anxiety disorders, ADHD, PTSD, sleep disorders, and chronic pain frequently co-occur with depression and actively undermine treatment outcomes when left unaddressed. Experts note that treating depression in isolation — without assessing the full clinical picture — is a primary driver of treatment resistance.

The clinical takeaway from the analysis is pointed: TRD is not simply depression that hasn't responded to enough medications. It is a biologically and clinically distinct presentation that demands a more targeted, multi-dimensional diagnostic approach.

Why Ketamine Enters the Picture

The mechanisms described in this expert analysis map directly onto why ketamine — and its FDA-approved derivative esketamine (Spravato) — has emerged as a leading option for TRD. Unlike SSRIs, ketamine acts on the glutamate system, the brain's primary excitatory neurotransmitter network. It works rapidly to restore synaptic connectivity in the prefrontal cortex and promotes neuroplasticity — essentially helping the brain form new, healthier communication pathways.

This mechanism is particularly relevant given what the Psychiatric Times panel describes: when the problem is dysfunctional circuitry rather than depleted serotonin, a serotonin drug is the wrong tool. Ketamine, by contrast, addresses the circuitry-level failure more directly. And it does so fast — often producing measurable relief within hours to days rather than the four to eight weeks required for traditional antidepressants to reach therapeutic levels.

Emerging research also suggests ketamine may have anti-inflammatory properties, potentially targeting one of the other biological contributors to TRD identified in this analysis. While this area of research is still developing, it adds another dimension to why ketamine therapy is increasingly seen as first-choice rather than last-resort for patients with confirmed treatment resistance.

What This Means for Patients and Caregivers

If you or someone you care for has been diagnosed with TRD — or suspects their depression may be treatment-resistant — the expert framework outlined in this analysis has several practical implications:

• Push for a comprehensive workup. Ask your psychiatrist or prescriber about inflammatory markers, thyroid and hormonal panels, and a formal comorbidity assessment. These factors are often skipped in routine depression evaluations but can significantly change the treatment path.
• Understand the TRD criteria. Most clinicians define TRD as failing at least two adequate antidepressant trials at appropriate doses and duration. If that describes your history, you may be a candidate for more targeted interventions — including ketamine therapy — that your current provider hasn't yet discussed.
• Ask specifically about ketamine and esketamine. Both IV ketamine (administered in ketamine clinics) and intranasal esketamine (Spravato, available in certified healthcare settings) are established options for TRD in 2026. Coverage for Spravato has expanded significantly, and many insurance plans now cover it for qualifying patients.
• Don't overlook comorbidities. If anxiety, PTSD, chronic pain, or sleep disruption are part of your experience, ensure these are being treated as part of an integrated care plan — not as afterthoughts to your depression treatment.

The growing scientific consensus reflected in this Psychiatric Times piece reinforces what patients with TRD have long known firsthand: depression that doesn't respond to standard medications isn't a personal failure or a mystery. It has identifiable biological underpinnings — and increasingly, it has real treatment options. For the full expert discussion, see the original article at Psychiatric Times.