What Is Treatment-Resistant Depression?

Depression is one of the most common medical conditions in the world — and yet for a significant portion of people who have it, standard first-line treatments don't work. If you've tried antidepressant after antidepressant and felt little or no improvement, you may have what clinicians call treatment-resistant depression. This is not a personal failing, and it is not a sign that your depression is beyond help. It is a recognized clinical condition with a growing range of effective, evidence-based treatment options.

How Is Treatment-Resistant Depression Defined?

The most widely used definition of treatment-resistant depression (TRD) is major depressive disorder that has not adequately responded to at least two antidepressant trials of adequate dose and duration within the current episode. "Adequate" typically means a therapeutic dose taken consistently for at least 4–6 weeks.

It's worth noting that the definition has some variability across institutions and insurers — some require two trials from different drug classes, and some include augmentation strategies in the count. But the core concept is the same: standard pharmacological treatments have been tried and have not produced a meaningful, sustained response.

Approximately 30% of people with major depression meet criteria for TRD. It represents one of the largest unmet needs in all of medicine.

Why Does TRD Happen?

TRD is not fully understood, but several factors are known to contribute:

• Biological variability: Traditional antidepressants (SSRIs, SNRIs, TCAs) work primarily by modulating serotonin, norepinephrine, or dopamine. For patients whose depression is driven more by glutamate dysregulation or neuroinflammatory pathways, these medications are targeting the wrong mechanism.
• Genetic factors: Pharmacogenomic testing can reveal how a patient metabolizes specific medications, explaining why some people have inadequate drug levels despite standard doses.
• Untreated comorbidities: Anxiety disorders, trauma, ADHD, substance use, chronic pain, and thyroid dysfunction can all maintain depression and reduce antidepressant response.
• Inadequate treatment trials: Many patients have never actually received an "adequate" trial — either the dose was too low, the duration was too short, or adherence was limited by side effects.

What Are the Treatment Options for TRD?

This is where the landscape has changed dramatically in the past decade. Several FDA-approved and strongly evidence-backed interventions now exist specifically for treatment-resistant depression:

TMS Therapy (Transcranial Magnetic Stimulation)

TMS uses magnetic pulses to directly stimulate the left dorsolateral prefrontal cortex — a brain region consistently underactive in depression. Because it works through electromagnetic stimulation rather than medication, it bypasses the pharmacological pathways that haven't been working. TMS is FDA-cleared, non-invasive, covered by most insurance plans, and has a strong evidence base with response rates around 50–60% and remission rates around 30–35% in TRD populations. Learn more about TMS →

Spravato (Esketamine)

Spravato is an FDA-approved nasal spray that works through NMDA receptor antagonism — a fundamentally different mechanism from all traditional antidepressants. It produces rapid antidepressant effects, often within hours to days, and is specifically approved for treatment-resistant depression. It is covered by most commercial insurance and Medicare when criteria are met. Learn more about Spravato →

Medication Augmentation

Before interventional treatments, or alongside them, augmentation strategies involve adding a second medication to an antidepressant to boost its effect. Common augmentation agents include lithium, atypical antipsychotics (aripiprazole, quetiapine, olanzapine), and thyroid hormone. These can be highly effective when matched carefully to the individual patient.

ECT (Electroconvulsive Therapy)

ECT remains one of the most effective treatments for severe, refractory depression — particularly in patients with psychotic features, catatonia, or acute suicidality. It has an undeservedly poor public image, largely based on outdated portrayals. Modern ECT is performed under brief general anesthesia and is far more targeted and tolerable than its historical reputation suggests. We refer patients who need ECT to Maine Medical Center.

Getting Evaluated at Portland Mental Health & Psychiatry

If you've tried multiple antidepressants without adequate relief, the first step is a thorough psychiatric evaluation to confirm the diagnosis, identify any contributing factors, and discuss your options. This is not a short appointment — our initial evaluations are 60–90 minutes, and we take the time to understand your full history before recommending a path forward.

One of the key advantages of our practice is that we offer TMS, Spravato, psychiatry, and therapy under one roof. If your current medications aren't working, you don't need to get a separate referral and start over somewhere else. Your psychiatrist works directly with our interventional team.