Treatment-Resistant Depression: What the Term Actually Means

"Treatment-resistant depression" sounds like a verdict on the person. It is not. It is a description of what has been tried and what happened, and the definition turns out to be narrower — and more useful — than the way the phrase gets thrown around.

Depression that has not lifted after one antidepressant is not treatment resistance. It is the ordinary course of treatment, which is why there is a second step, and a third.

What the definition actually says

No single definition commands universal agreement, which is worth knowing before anyone quotes one at you with confidence. But the version used in most clinical practice and in most of the trials regulators rely on is broadly this: an inadequate response to two or more antidepressant treatments, given at an adequate dose, for an adequate duration, in the current episode of depression.

Three phrases there do the real work.

Two or more. Not one. Not "it didn't seem to help much."

Adequate dose. Many courses are started low, deliberately, to limit early side effects, and then never increased. A trial that stayed at the starting dose is not a trial of the drug.

Adequate duration. Antidepressants are slow. Some effects appear within a couple of weeks, but the full picture generally takes six to eight weeks at a therapeutic dose, and for some people longer. Stopping at week three tells you almost nothing.

Why "adequate trial" is where most cases fall apart

Take a proper medication history from someone who has been told they have treatment-resistant depression and a fair number of the previous trials do not meet the standard. The dose was never optimised. The course was cut short by side effects in the first fortnight. The prescription was collected once and never refilled. None of that is a criticism of the patient — the first few weeks are the hardest part — but it changes the next step. If a drug was never properly tried, trying it properly may beat moving to something more intensive.

What usually gets tried, and roughly in what order

Sequencing varies by clinician and by patient, but the general shape is consistent.

First line is usually an SSRI, sometimes an SNRI, chosen with an eye to side-effect profile, interactions and what has worked for the person before or in their family. Psychotherapy — CBT or another structured, evidence-based approach — belongs here too, alongside medication rather than after it. The combination generally outperforms either alone. A partial response is usually met by optimising the dose and giving it time; no response at all makes switching more sensible than pushing.

Second line is typically a switch, within class or to a different mechanism — an SNRI, bupropion, mirtazapine. Where there was a partial response, augmentation is often preferred: adding lithium, an atypical antipsychotic licensed for the purpose, or thyroid hormone to the existing antidepressant rather than replacing it.

It is at the point where two adequate trials have genuinely failed that the term starts to apply and the conversation changes. We go through the ketamine end of it in our full guide to ketamine for treatment-resistant depression.

The things commonly missed before resistance is concluded

This is the most useful part of the assessment and the part most often skipped. Several conditions produce depression that does not respond to antidepressants, because the antidepressant is not addressing what is driving it.

Undiagnosed bipolar disorder

Bipolar depression looks like unipolar depression from the inside. People present in the depressed phase, because that is the phase that makes you seek help, and hypomanic periods are often remembered as simply feeling well. Antidepressants used alone in bipolar depression frequently do not work and can destabilise mood. A careful history asks about periods of reduced need for sleep, unusual energy, uncharacteristic spending or risk-taking, and about family history.

Thyroid disease

Hypothyroidism produces fatigue, low mood, slowed thinking and weight change. It is straightforward to test for and straightforward to treat, and it is a standard part of a depression workup for exactly that reason.

Obstructive sleep apnoea

Chronically fragmented sleep produces low mood, poor concentration and daytime exhaustion that no antidepressant will fix. Sleep apnoea is under-diagnosed generally and particularly under-considered in people already carrying a psychiatric diagnosis. We wrote about why sleep gets treated first surprisingly often in the piece on sleep and mental health.

Alcohol and other substance use

Regular alcohol use will blunt the effect of an antidepressant and worsen sleep, and people routinely under-report it — not out of dishonesty but because the drinking has become unremarkable. This has to be asked about directly and answered honestly for the assessment to be worth anything.

Other medical and situational contributors

Anaemia, vitamin B12 deficiency, chronic pain, some prescribed medications, and untreated ADHD all show up here. So does an unresolved situation: a job that is grinding a person down, a bereavement, caregiving with no relief. Situational exhaustion and clinical depression can look similar and respond to different things — we set out the differences in burnout or depression.

What opens up after two adequate trials

More than most people expect, and none of it is a last resort in the way the phrase implies.

Augmentation. Adding a second agent to an antidepressant that is partly working. Lithium and certain atypical antipsychotics have the longest track record, and both require monitoring.

Structured psychotherapy, properly delivered. If therapy was never part of the picture, or was a handful of sessions years ago, this is not a small option.

Transcranial magnetic stimulation (TMS). Non-invasive, delivered in a clinic over several weeks, FDA-cleared for depression that has not responded to medication.

Esketamine (Spravato). FDA-approved for treatment-resistant depression, given as a nasal spray under direct supervision in a certified healthcare setting, with a monitoring period afterwards. It is not something you take home. Other forms of ketamine used for depression are prescribed off-label, which is a legitimate practice but a different regulatory situation entirely. The distinction is constantly blurred in advertising, and we pull it apart in Spravato vs generic ketamine.

Electroconvulsive therapy. Still the most effective treatment available for severe depression, still carrying a public reputation formed decades before modern technique and anaesthesia. It remains an appropriate option, particularly where depression is severe or urgent.

Eligibility for any of these is decided by a clinician after screening, and people are screened out. For ketamine and esketamine specifically, a history of psychosis or a psychotic disorder, certain cardiovascular conditions including poorly controlled blood pressure, a history of substance misuse, and pregnancy all weigh against treatment. That screening is the treatment being taken seriously, not an obstacle to it. Our ketamine therapy service page sets out what the assessment covers.

How to use the term when you talk to a clinician

Say what happened rather than what it is called. "I've been on sertraline and venlafaxine, sertraline at 100mg for four months, venlafaxine I stopped at week three because of the nausea" gives a clinician something to work with. "I have treatment-resistant depression" does not.

Be alert, too, to how the phrase is used commercially. Clinics selling a specific intervention have an interest in describing more people as treatment-resistant, because that is who the intervention is for. A practice willing to tell you a previous drug deserves a proper trial before anything else is offered is behaving correctly. One that reaches the diagnosis from a web form is not — see how to spot a prescription mill.

Depression that has resisted two treatments is a harder clinical problem, not an unsolvable one. The sequence takes longer than anyone wants it to, and that is not evidence that nothing will work. To talk through where you are in it, you can book a consultation with a licensed clinician.