Treatment-Resistant Depression (TRD)

The short version

●Treatment-resistant depression (TRD) is most commonly defined as failure to achieve adequate response to two or more adequate trials of antidepressants from different classes — adequate dose, adequate duration (usually 6-8 weeks), and adequate adherence.
●STAR*D was the foundational naturalistic study: 4,041 patients with major depression sequenced through up to four treatment steps. Cumulative remission was approximately 67%, but Pigott's 2023 reanalysis using stricter criteria found rates considerably lower than originally published.
●TRD is not rare — meaningful estimates suggest 30-40% of all MDD patients meet TRD criteria across the course of their treatment.
●Ketamine (off-label, racemic) and esketamine (Spravato, FDA-approved for TRD) are the rapid-acting options with the most established evidence base. Both work through NMDA receptor antagonism and downstream glutamate-driven plasticity.
●Other TRD strategies: augmentation (lithium, thyroid hormone, atypical antipsychotic, bupropion), switch to different antidepressant class (MAOI, TCA), neurostimulation (rTMS, ECT, VNS, DBS), psychotherapy enhancement.
●STAR*D-style sequential trials remain the framework, but rapid-acting agents are reasonably considered earlier in the sequence — especially for patients with prominent suicidality where the 4-8 week SSRI onset is clinically untenable.

Clinical definition

There is no single universally accepted definition of TRD. The most common operational definition: failure to achieve adequate response (typically ≥50% reduction in symptom score) after at least two adequate trials of antidepressants from different mechanistic classes during the current major depressive episode. "Adequate" requires three components: dose at the therapeutic range, duration of at least 6-8 weeks at therapeutic dose, and confirmed adherence. ICD-10 and DSM-5-TR do not give TRD a distinct diagnostic code; it is treated as a specifier on the underlying mood disorder. The Maudsley Staging Method (Fekadu and colleagues) provides a more granular five-stage system based on episode duration, symptom severity, and treatment failures. Recently, "difficult-to-treat depression" (DTD) has been proposed as a less judgmental alternative term that captures the same population without implying the disorder is solely resistant — Rush 2022 (Psychological Medicine) articulates the rationale. The clinical implications of the TRD designation are substantial: longer-duration treatment plans, earlier consideration of augmentation and rapid-acting agents, more frequent treatment monitoring, and explicit discussion of realistic outcome targets that may include "response" rather than "remission" for the most severely treatment-resistant.

How it differs from related conditions

vs. First-line major depressive disorder

MDD before TRD designation: any episode of major depression at first presentation. TRD designation applies after at least two adequate antidepressant trials have failed. Many patients labeled "TRD" have not actually had two adequate trials — sub-therapeutic doses or premature discontinuation can mimic TRD without meeting the definition.

vs. Pseudoresistant depression

Patients labeled as treatment-resistant who actually have sub-therapeutic dosing, inadequate duration of trials, undisclosed non-adherence, undiagnosed bipolar spectrum, or untreated comorbidity (substance use, hypothyroidism, sleep apnea). Estimated to account for a meaningful proportion of apparent TRD. Distinguishing matters: pseudoresistant depression often responds to properly executed first-line care.

vs. Bipolar depression misdiagnosed as TRD

Common pitfall. Bipolar 2 patients often present in depressive phase with no spontaneous report of hypomania (which they may not recognize as pathological). Repeated antidepressant failures plus rapid cycling or early-life mood instability should prompt bipolar reassessment with structured tools (MDQ, structured interview). Treatment changes substantially if bipolar.

vs. Persistent depressive disorder (PDD/dysthymia)

PDD is chronic (≥2 years) lower-grade depression; TRD is treatment-failure after adequate trials. PDD patients can also be treatment-resistant (and often are), but the duration criterion for PDD does not require failed treatment. Distinguishing matters because PDD has lower baseline response rates and modified expectations.

First-line treatments

Esketamine intranasal (Spravato)

FDA-approved for TRD in 2019. Intranasal S-enantiomer of ketamine, administered in clinic under observation. Twice-weekly induction (4 weeks), then weekly, then every 1-2 weeks. REMS program (mandatory monitoring). Effect sizes in TRD trials are clinically meaningful; response sustained with continued dosing. Insurance coverage variable. Cost considerations.

Racemic ketamine (off-label)

IV, IM, oral, sublingual, intranasal formulations available. Off-label for TRD but the established evidence base predates esketamine's approval — Murrough 2013 AJP and many subsequent trials demonstrate rapid antidepressant effect. Mechanism shared with esketamine (NMDA receptor antagonism). Lower cost than esketamine; more route flexibility; can be delivered at home with appropriate medical oversight.

Lithium augmentation

Classic TRD augmentation strategy. Added to ongoing antidepressant at target serum level 0.4-0.8 mEq/L. Requires monitoring (thyroid, renal, lithium levels). Effect sizes in TRD trials are clinically meaningful. Useful particularly when bipolar spectrum cannot be ruled out — lithium has activity in both unipolar and bipolar depression.

Atypical antipsychotic augmentation (aripiprazole, quetiapine, olanzapine-fluoxetine)

FDA-approved augmentation indications for TRD. Aripiprazole 2.5-15mg or quetiapine XR 150-300mg added to ongoing antidepressant. Effect sizes substantial but side effect burden (metabolic, weight, sedation, EPS) is non-trivial. Reserve for patients with adequate antidepressant trials who have plateaued.

Switch to different antidepressant class

After SSRI failure, switch to SNRI; after SNRI failure, switch to bupropion or mirtazapine; after multiple class failures, consider TCAs or MAOIs. Switch vs augmentation choice depends on patient history, side effect tolerability, and whether partial response has occurred. STAR*D-style sequencing is the framework.

rTMS (repetitive transcranial magnetic stimulation)

FDA-approved for TRD. Daily outpatient sessions (4-6 weeks). Non-invasive, no medication interaction, no systemic side effects. Effect sizes moderate; response rates 30-50%. Insurance coverage typically requires documented antidepressant failures. Theta-burst protocols shorten treatment course.

ECT (electroconvulsive therapy)

Highest single-treatment efficacy in severe TRD, particularly with psychotic features, catatonic features, or acute suicide risk. Response rates 60-80% in severe TRD trials. Cognitive side effects (memory) are the major concern; modern bilateral or right unilateral protocols minimize. Reserved for the most severe presentations.

When standard treatments fail

After multiple antidepressant trials, augmentation, and rapid-acting agents have failed, escalation includes: VNS (vagus nerve stimulation, FDA-approved for chronic TRD), DBS (deep brain stimulation, investigational), MAOI trial in specialty care, intensive psychotherapy combined with novel pharmacologic strategies, and reassessment of underlying diagnosis (occult bipolar, undiagnosed medical comorbidity, accumulated medication-induced symptoms). At this level of treatment resistance, "remission" may not be a realistic short-term goal; the clinical conversation often shifts to acceptable response (≥50% symptom reduction) and functional recovery rather than complete symptom elimination. Specialty TRD centers exist (academic mood disorder programs, NIMH-supported clinical research networks) and offer trial access plus comprehensive multidisciplinary assessment.

Where ketamine fits

TRD is THE clinical niche where ketamine has the most established evidence base. The Murrough 2013 AJP RCT demonstrated rapid antidepressant effect in TRD patients within 24 hours; multiple subsequent trials have replicated and extended these findings. Esketamine's 2019 FDA approval for TRD was based on this body of evidence. Mechanism: NMDA receptor antagonism leads to downstream glutamate surge and BDNF-mediated synaptic plasticity, producing rapid mood improvement distinct from the monoamine-modulating mechanism of conventional antidepressants. Critical considerations for TRD patients: rapid effect is well-established (hours to days), durability of single-session response is short (typically 1-2 weeks), and a maintenance plan is essential for sustained benefit. Most TRD patients require a course of 4-6 sessions induction followed by maintenance dosing at decreasing frequency. Pairing with concurrent psychotherapy improves durability. The Sanacora 2017 APA consensus statement provides framework for clinical use.

Where this fits with Tovani

TRD is the primary clinical indication Tovani addresses. The eligibility process requires documented failure of at least two adequate antidepressant trials at therapeutic doses for at least 6-8 weeks each. Patients are evaluated for bipolar spectrum (MDQ screening) because antidepressant-induced cycling in undiagnosed bipolar 2 is a common cause of apparent TRD that requires different treatment. Tovani delivers oral ketamine (racemic) for at-home use with physician oversight, integration support via the KetAI session companion, and concurrent recommendations for psychotherapy (typically IFS, EMDR, or KAP-trained therapists). Most TRD patients begin with a 4-6 session induction followed by maintenance at decreasing frequency over the subsequent months.

Check eligibility The science behind ketamine

Frequently asked

How many medications do I have to try before I have TRD?

The most common operational definition is failure of at least two adequate antidepressant trials from different mechanistic classes. "Adequate" means therapeutic dose, at least 6-8 weeks of treatment, and confirmed adherence. Many patients labeled as treatment-resistant have not actually completed two adequate trials — sub-therapeutic dosing or premature discontinuation is common. Reviewing the actual treatment history matters.

Is ketamine better than esketamine?

Both work through the same mechanism (NMDA antagonism). Esketamine (Spravato) is FDA-approved for TRD specifically; racemic ketamine is off-label but has a longer evidence base. Practical differences: esketamine requires in-clinic administration under observation; racemic ketamine is more flexible (oral, IM, IV, sublingual, intranasal). Cost favors generic ketamine. Insurance coverage favors esketamine. Patient access and physician practice patterns vary.

How long will the ketamine effect last?

Single-session response is short — typically 1-2 weeks. Sustained benefit requires a course of multiple sessions during induction (typically 4-6 over 2-4 weeks), followed by maintenance at progressively longer intervals. Pairing with concurrent psychotherapy improves durability. Some patients achieve sustained remission; others require ongoing maintenance.

Why didn't my STAR*D-style sequence work?

STAR*D demonstrated cumulative remission of approximately 67% after up to four treatment steps; the Pigott 2023 reanalysis found this was likely overestimated. A meaningful minority of TRD patients do not achieve remission with conventional sequencing alone, which is precisely why rapid-acting agents (ketamine, esketamine) and neurostimulation (rTMS, ECT) entered the treatment landscape. Sequential failure does not mean nothing will work — it means a different mechanism may be required.

Will I need ketamine forever?

Variable. Some patients achieve sustained remission after an induction course and gradual taper of maintenance dosing. Others need long-term maintenance at low frequency (every 2-4 weeks). The honest answer is that durability cannot be predicted in advance for any individual patient. Concurrent psychotherapy and lifestyle factors (sleep, exercise, substance use) significantly influence long-term outcomes.

References

Murrough JW et al. 2013, American Journal of Psychiatry — Randomized controlled trial of ketamine in treatment-resistant depression — rapid antidepressant effect within 24 hours, foundational evidence supporting ketamine's rapid-acting mechanism in TRD specifically. (PMID 23982301)
Sanacora G et al. 2017, JAMA Psychiatry — APA consensus statement on the use of ketamine in the treatment of mood disorders — clinical framework for ketamine use in TRD including patient selection, dosing, monitoring, and combination with psychotherapy. (PMID 28249076)
Cipriani A et al. 2018, Lancet — Network meta-analysis of 21 antidepressants in adult depression — comparative effect sizes informing sequencing decisions in TRD, particularly the choice of switch versus augmentation strategies. (PMID 29477251)
Rush AJ et al. 2022, Psychological Medicine — Clinical research challenges posed by difficult-to-treat depression — Rush and colleagues argue for "difficult-to-treat depression" terminology and reframe outcome targets toward functional recovery rather than complete remission in severe TRD. (PMID 34991768)
Pigott HE et al. 2023, BMJ Open — Reanalysis of STAR*D treatment remission rates — finds rates considerably lower than originally published when stricter criteria are applied, with implications for setting realistic expectations in TRD treatment. (PMID 37491091)

Last reviewed by Dr. Ben Soffer, DO on May 27, 2026. This page is educational and not a substitute for clinical evaluation. A physician determines whether ketamine therapy is appropriate for your specific situation.