Treatment-Resistant Depression: When Antidepressants Aren't Working

TRD has a clinical definition: failure to respond to at least two adequate antidepressant trials. “Adequate” means a therapeutic dose taken for at least 6–8 weeks. This matters because a lot of treatment “failures” are actually inadequate trials — doses that were too low, durations that were too short, or medications that were stopped before they had a chance to work.

TRD is more common than most people realize. Approximately 30% of people with major depressive disorder (MDD) do not achieve remission with initial antidepressant treatment. This is not a rare edge case — it is a predictable pattern that has driven decades of research into alternative and augmentation approaches.

Why does TRD happen?

• Genetics and pharmacogenomics — Variations in genes like CYP2D6 and CYP2C19 affect how your liver metabolizes psychiatric medications. Someone who is a “rapid metabolizer” may clear a medication too quickly for it to reach therapeutic levels, even at standard doses.
• Underlying diagnostic picture — Antidepressants are frequently prescribed for what turns out to be bipolar II disorder, where antidepressant monotherapy is not only ineffective but can destabilize mood further. Misdiagnosis is a significant driver of apparent TRD.
• Medical contributors — Untreated hypothyroidism, sleep apnea, vitamin D deficiency, chronic pain, and inflammatory conditions can all sustain depressive symptoms that antidepressants alone cannot overcome. If these have not been evaluated, they should be.
• Comorbid anxiety, trauma, or substance use — When depression co-occurs with PTSD, severe anxiety, or active substance use, antidepressants frequently underperform until those comorbidities are also addressed.

Before escalating to more complex interventions, a systematic review of what has actually been tried — and how — is essential. Many apparent TRD cases resolve when these questions are addressed.

Was the dose truly adequate?

Many prescribers start at a low dose and do not push to a therapeutic dose because patients report tolerability issues at low doses or express reluctance to increase. A therapeutic dose of sertraline is often 150–200 mg, not 50 mg. Fluoxetine may require 40–60 mg for depression. If you have only ever been on the starting dose, this is the first conversation to have.

Was it given long enough?

Six to eight weeks at a therapeutic dose — not six to eight weeks total, including the weeks at subtherapeutic doses during titration. The full antidepressant effect for some people takes 10–12 weeks. Stopping at week five because “it isn't working” is one of the most common reasons genuine treatment failures are manufactured.

Is there an underlying bipolar component?

Bipolar II disorder is significantly underdiagnosed, particularly in people who present with depression. Hypomania is often not recognized — patients and even some providers do not identify elevated energy, decreased sleep need, and increased productivity as a symptom of illness. If you have had periods of uncharacteristically high energy, reduced sleep without fatigue, or significant impulsivity alternating with depression, this should be evaluated before adding more antidepressants.

Are anxiety, trauma, or substance use driving the picture?

Depression that is driven by unprocessed trauma, active PTSD, or severe anxiety often requires targeted treatment for those conditions — not just antidepressant titration. Similarly, alcohol use (even moderate, regular use) is strongly depressogenic and will blunt or eliminate antidepressant response. Substance use must be part of the evaluation.

Have medical contributors been ruled out?

A complete TRD workup typically includes: thyroid panel (TSH, free T3/T4), CBC, comprehensive metabolic panel, vitamin D level, and screening for sleep apnea. Treating hypothyroidism or sleep apnea can sometimes resolve depression that appeared medication- resistant.

Once inadequate trials have been ruled out, the clinical approach to TRD involves augmentation, switching, or combination strategies — each with its own evidence base.

Augmentation strategies

Augmentation means adding a second medication to the existing antidepressant rather than replacing it. The most evidence-based options:

• Atypical antipsychotics — Aripiprazole (Abilify), quetiapine (Seroquel), and brexpiprazole (Rexulti) all have FDA approval as adjunctive treatments for MDD. They augment antidepressant response through dopamine and serotonin receptor modulation. Response rates with augmentation are meaningfully higher than continuing antidepressant monotherapy. Side effect profiles differ: weight gain is more common with quetiapine, akathisia (restlessness) is possible with aripiprazole.
• Lithium augmentation — One of the oldest and most evidence-based augmentation strategies. Lithium added to a tricyclic or SSRI has demonstrated response rates of 40–65% in studies of TRD. It requires monitoring (blood levels, kidney, thyroid) but remains a standard option. Often underused because prescribers are not trained in lithium management.
• Thyroid hormone (T3) augmentation — Adding liothyronine (T3) to an antidepressant, even in patients without thyroid disease, has evidence for improving antidepressant response. The mechanism is not fully understood but is thought to relate to thyroid hormone's role in serotonin receptor sensitivity.

Switching strategies

If augmentation is not appropriate or tolerated, switching to a different medication class may be warranted:

• SNRIs (venlafaxine, duloxetine, desvenlafaxine) — add norepinephrine reuptake inhibition alongside serotonin; may work for SSRIs that did not
• Bupropion (Wellbutrin) — dopamine and norepinephrine mechanism; particularly useful when fatigue, low energy, or concentration are predominant; activating, so timing matters
• MAOIs — monoamine oxidase inhibitors (phenelzine, tranylcypromine) are among the most effective antidepressants in treatment-resistant cases but are rarely used due to dietary restrictions (tyramine) and drug interaction risks. In the right patient with the right prescriber oversight, they can be transformative.

Combination strategies

• SSRI + bupropion — a common and well-tolerated combination that adds dopaminergic effects to serotonergic coverage; also useful when sexual side effects from SSRI monotherapy are significant
• SSRI + mirtazapine (“California Rocket Fuel”) — mirtazapine adds noradrenergic and histaminergic activity, presynaptically enhancing serotonin release; the combination has shown superior response rates vs. either alone for severe TRD in several trials; sedating properties of mirtazapine can be an advantage for patients with insomnia-driven depression

For patients who have not responded to multiple medication trials, several newer and more intensive treatments have strong evidence bases. These are not last resorts — they are appropriately matched tools for a specific clinical picture.

Esketamine (Spravato) — FDA-approved for TRD

Esketamine is an intranasal ketamine derivative with FDA approval specifically for treatment-resistant depression and major depressive disorder with suicidal ideation. It works on NMDA glutamate receptors — a completely different mechanism from all oral antidepressants — and can produce rapid antidepressant effects, sometimes within hours.

Sessions are administered in a certified healthcare setting (not at home) due to monitoring requirements; patients self- administer the nasal spray while observed for two hours for blood pressure changes and dissociative effects. A typical course is twice weekly for four weeks, then weekly, then biweekly. Insurance coverage has expanded but can still be challenging; prior authorization is usually required. Not appropriate for patients with active psychosis, uncontrolled hypertension, or a history of aneurysmal vascular disease.

TMS — Transcranial Magnetic Stimulation

TMS uses magnetic pulses to stimulate underactive regions of the prefrontal cortex — areas consistently implicated in depression — without the systemic side effects of medication. Response rates are approximately 50–60%, with remission rates around 30–35%. A standard course is 36 sessions over 6–9 weeks, typically 20–40 minutes each on weekdays. Patients remain awake and can drive themselves home. Side effects are usually limited to mild scalp discomfort at the treatment site.

TMS has FDA clearance for MDD and OCD. Major insurance carriers have expanded coverage significantly; many now cover it after failure of two or more adequate antidepressant trials — which is exactly the TRD definition. It is not appropriate for patients with metal implants in or near the head (cochlear implants, certain aneurysm clips).

ECT — Electroconvulsive Therapy

ECT is the most effective treatment available for severe, treatment-resistant depression — response rates in the range of 70–90% in appropriately selected patients. This is not a last resort; it is an intervention that is frequently delayed too long because of stigma, not evidence.

Modern ECT bears no resemblance to its historical depiction. It is performed under general anesthesia and muscle relaxant. The patient feels nothing. Sessions are typically three times per week for 3–4 weeks. The main side effect is short-term memory disruption, which typically resolves after treatment ends. ECT is particularly indicated for severe TRD, psychotic depression, catatonia, severe suicidality, and TRD in pregnancy when medication risks are unacceptable.

Ketamine IV Infusions (off-label)

IV ketamine (racemic ketamine, as opposed to the FDA-approved esketamine nasal spray) is used off-label at ketamine infusion clinics for TRD. Evidence is promising — rapid antidepressant effects similar to esketamine — but it is not covered by insurance and costs $400–$800 per infusion out of pocket. Response is typically not sustained without maintenance sessions. If considering this, verify the clinic has appropriate medical oversight and a clear protocol for ongoing care.

Medication alone — even with augmentation and advanced interventions — leaves a meaningful gap when compared to medication plus psychotherapy for TRD. The combination consistently outperforms either alone. This is not an opinion; it is the finding of multiple large randomized controlled trials.

CBT for depression

Cognitive Behavioral Therapy structured specifically for depression targets the thought patterns (cognitive distortions, negative attributional style) and behavioral patterns (withdrawal, inactivity, avoidance) that sustain depression independently of biological factors. In TRD, where biology alone may be resistant to intervention, addressing these maintaining factors is often what moves the needle.

Behavioral activation

Behavioral activation is one of the most studied and efficacious components of CBT for depression. It works by systematically reintroducing activities that previously provided a sense of pleasure or accomplishment — counteracting the withdrawal-depression cycle. It sounds simple because it is, mechanically. The clinical challenge is motivation, which is why therapist guidance matters.

MBCT for recurrence prevention

Mindfulness-Based Cognitive Therapy (MBCT) is specifically designed for people with recurrent depression and has strong evidence for reducing relapse risk in patients who have had three or more depressive episodes. It does not treat acute TRD as directly as standard CBT, but for people in remission who want to stay in remission, it is one of the strongest tools available.

If your antidepressant is not working, these are the questions worth asking at your next appointment. You have the right to ask them. A good prescriber will welcome them.

• “Have we tried augmentation?” — If you have been on an antidepressant for several months with partial response, adding an augmenting agent (aripiprazole, quetiapine, lithium) is a standard, evidence-based next step. Ask whether this has been considered and why or why not.
• “Am I a candidate for esketamine or TMS?” — If you have failed two or more adequate trials, you may meet criteria for both. Ask your prescriber to evaluate candidacy and, if appropriate, to initiate a referral.
• “Should I see a psychiatrist for a second opinion?” — Complex TRD is appropriately managed by psychiatry, not primary care. If you are seeing a PCP or NP who is not specialized in psychiatry, requesting a psychiatric consultation is not insulting — it is appropriate care navigation.
• “Is there a pharmacogenomic test that might explain why meds aren't working?” — Tests like GeneSight or similar pharmacogenomics panels assess how your genes affect metabolism of specific psychiatric medications. They are not diagnostic tools but can identify specific medications you are likely to metabolize too quickly or too slowly, informing medication selection. Insurance coverage varies.
• “Have we fully ruled out bipolar II?” — If you have ever had periods of significantly elevated energy, decreased sleep need, or impulsivity, this warrants explicit discussion. Bipolar II depression is treated differently than unipolar MDD, and antidepressant monotherapy can worsen the course.