Why Ketamine Works Differently Than Other Antidepressants
To understand what affects ketamine’s response rate, it helps to understand how it works. Most standard antidepressants — SSRIs (selective serotonin reuptake inhibitors) and SNRIs (serotonin-norepinephrine reuptake inhibitors) — target the monoamine system, increasing availability of serotonin or norepinephrine over weeks of daily dosing. IV ketamine takes a different route entirely. It works primarily by blocking NMDA receptors in the glutamate system — the brain’s primary excitatory neurotransmitter network — producing rapid antidepressant effects through a mechanism that conventional medications do not engage (PMC: NMDA Receptor / Glutamate System).
This distinction matters clinically. When depression has not responded to multiple serotonin-targeted treatments, it is often a signal that the neurobiology involved extends beyond the monoamine pathways those medications reach. Ketamine’s glutamate-based mechanism makes it effective for exactly that population — but it also means that the factors affecting whether ketamine works are different from those affecting whether an SSRI works. Candidacy is not simply about diagnosis. It is about the full clinical picture.
Who Tends to Respond Well
Research on ketamine’s antidepressant effects consistently shows significant and rapid response in patients with treatment-resistant major depression — those who have not found relief through prior medication trials (PMC: Antidepressant Efficacy in Treatment-Resistant Depression). Within that population, certain clinical characteristics are associated with stronger responses.
Patients with more acute, episodic depression tend to respond more robustly than those with very long-standing, chronic depression, though both populations can benefit. Patients who do not have active contraindications — including uncontrolled blood pressure, unstable heart disease, untreated thyroid disease, active substance use, current manic phase of bipolar disorder, or active psychotic symptoms — are better positioned for a full, safely titrated course. Patients who are able to complete all six infusions in the recommended two-week window, rather than spreading them out over a longer period, tend to see stronger cumulative effects.
Part of what makes our response rate as high as it is — over 80% in our practice — is the degree of individualization in every infusion. We do not run a fixed protocol. Concentration, infusion duration, and pre-medications are adjusted for each patient and across each infusion based on real-time monitoring and response. That titration process is something Dr. Prashad, a board-certified psychiatrist who founded the American Society of Ketamine Physicians, Psychotherapists and Practitioners, conducts personally and adjusts dynamically throughout the course.
Ketamine also promotes neuroplasticity — the brain’s capacity to form and strengthen new neural connections — and may increase brain-derived neurotrophic factor (BDNF), a protein essential for neuron growth and long-term mood regulation (PMC: Ketamine Increases BDNF). Patients who are engaged in supportive therapy or structured follow-up during and after the infusion series may extend and deepen these neuroplastic effects.
What Can Limit Response
Being direct about this is something we consider part of good care. Ketamine is not effective for everyone, and certain factors are associated with a more limited response.
Active contraindications represent the clearest category. Uncontrolled blood pressure and unstable cardiac conditions create safety concerns that must be addressed before ketamine is appropriate. Untreated thyroid disease can sustain depressive symptoms independently, meaning ketamine may not produce its full effect until that underlying condition is managed. Active substance use — particularly with alcohol or substances that interact with NMDA receptors — can blunt ketamine’s mechanism of action or create unsafe combinations. These are not arbitrary restrictions; they reflect the biology of how ketamine works and where it is safe to use.
Beyond contraindications, certain psychiatric presentations are associated with reduced response. Patients currently in a manic phase of bipolar disorder are not candidates for ketamine. Patients with active psychotic features require careful evaluation. For patients with bipolar depression in a depressive phase, IV ketamine can be an appropriate option — but the clinical context needs to be assessed carefully and the full psychiatric picture considered.
Patients whose depression is sustained by an undertreated medical condition — thyroid dysfunction, chronic inflammation, significant sleep disruption — may find that ketamine produces limited relief until that underlying driver is addressed. This is one reason our evaluation process looks at the full clinical picture before recommending any treatment.
What Happens When the First Course Isn’t Enough
A non-response to the initial infusion series is not a closed door. It is information that shapes what we try next, and we treat it that way.
For patients who show partial response — meaningful improvement that does not fully meet their goals — we consider whether adjusting the dosing protocol, extending the series, or adding a complementary treatment may close the gap. The IV Ketamine + Deep TMS combination protocol, for example, is specifically designed for patients with significant anxiety alongside depression and for those who have not responded to either treatment individually. Ketamine enhances neuroplasticity, which creates conditions that may allow Deep TMS to produce more durable and complete effects. Clinical data from our own practice supports this synergistic relationship.
For patients who do not respond to IV ketamine, SPRAVATO® (esketamine nasal spray) — which is FDA-approved for treatment-resistant depression and for major depressive disorder with acute suicidal ideation — works through a related but distinct mechanism and may produce a response where IV ketamine has not. The delivery method, dosing structure, and clinical supervision requirements differ between the two, and some patients respond to one but not the other.
Deep TMS is another distinct option. It works through magnetic stimulation of brain circuits rather than pharmacology and carries no systemic side effects. For patients who have not responded to ketamine and prefer a non-medication approach, Deep TMS represents a meaningfully different mechanism and a different candidacy profile.
We do not present any of these alternatives as fallbacks. Each is a primary, evidence-based treatment in its own right. The sequence and combination of treatments is something we determine collaboratively based on each patient’s history, response, and goals — not on a fixed algorithm.
Addressing Two Honest Barriers
The fear of wasting money on something that might not work. This is one of the most common concerns we hear, and it deserves a direct answer. IV ketamine is not covered by insurance, and at $650 per infusion — with the sixth infusion at a 50% discount when the full series of six is completed — the cost of a full course is real. Financing is available for patients who qualify. What we can say honestly is that the response rate in our practice is over 80%, and most patients know within the first one or two infusions whether ketamine is likely to help them. That early signal means patients are not committed to a full course without information. We discuss all of this before treatment begins, because we believe financial transparency is part of informed consent.
The fear that a non-response means nothing will ever work. Patients who contact us after failing multiple antidepressants, and sometimes after failing other interventional treatments as well, sometimes carry the understandable concern that their depression is simply untreatable. It is not. A non-response to IV ketamine is clinical information — it tells us something specific about mechanism — not a verdict on whether recovery is possible. The options available for treatment-resistant depression have expanded substantially, and most patients who come to us have not exhausted all of them. Results vary by individual, and the evaluation conversation is always about what has not been tried yet rather than what has already failed. Discussing your options with a provider who specializes in this population is the most direct way to find out what your next step is.
Frequently Asked Questions
How quickly will I know if IV ketamine is working? Most patients notice the early signal of response within the first one or two infusions — often within hours of the first treatment. Antidepressant changes are distinct from the infusion experience itself and may include shifts in mood, energy, and the quality of depressive thinking. If there is no meaningful response after two infusions, we have a direct conversation about whether continuing the series is the right call or whether a different approach may be a better fit.
Does ketamine work better for some types of depression than others? Clinical research supports its strongest evidence base for treatment-resistant major depression — depression that has not responded to at least two prior antidepressant trials at adequate doses (PMC: Antidepressant Efficacy in Treatment-Resistant Depression). It is also used at our practice for bipolar depression, postpartum depression, PTSD, and severe anxiety. Results vary across and within these populations, and candidacy depends on the full clinical picture rather than diagnosis alone.
What medical conditions might make IV ketamine a poor fit for me? Uncontrolled blood pressure, unstable heart disease, untreated thyroid disease, active substance use, current manic phase of bipolar disorder, and active psychotic symptoms are contraindications we screen for carefully. These are not arbitrary exclusions — they reflect real safety and efficacy considerations. Our evaluation process identifies these factors before treatment is recommended, and in some cases addressing an underlying condition first may make ketamine a viable option later.
What if I respond partially but not fully? Partial response is meaningful and worth building on. We may discuss adjusting the dosing protocol, the timing of maintenance infusions, or adding a complementary treatment such as Deep TMS or Ketamine-Assisted Psychotherapy (KAP) to help extend and deepen the initial response. We stay engaged with patients throughout the process and do not treat partial response as a final outcome.
Is SPRAVATO® an option if IV ketamine doesn’t work? Yes. SPRAVATO® is an FDA-approved esketamine nasal spray for treatment-resistant depression and for major depressive disorder with acute suicidal ideation or behavior. While it works through a related mechanism to IV ketamine, the delivery method, dosing schedule, and clinical context differ — and some patients respond to one where the other produced limited effect. We discuss this option explicitly when IV ketamine has not produced adequate relief.
Key Takeaways
- IV ketamine produces a meaningful antidepressant response in approximately 70 to 80 percent of patients with treatment-resistant depression; our practice’s personal response rate exceeds 80%, supported by individualized dosing and real-time titration.
- Ketamine works through the glutamate system via NMDA receptor blockade — a mechanism distinct from SSRIs and SNRIs — which is why it is effective for many patients whose depression has not responded to monoamine-targeted treatments.
- Certain factors can limit response, including active contraindications, undertreated medical conditions, and psychiatric presentations such as active mania or psychosis; our evaluation process identifies these before treatment begins.
- A non-response to the initial IV ketamine course is clinical information, not a verdict; SPRAVATO®, Deep TMS, and the IV Ketamine + Deep TMS combination protocol are all primary options with distinct mechanisms that may produce results where IV ketamine alone has not.
- Results vary by individual, and the decision to pursue IV ketamine — including a transparent conversation about cost, response likelihood, and alternatives — is made collaboratively during consultation.
IV ketamine is one of the most effective tools we have for treatment-resistant depression, and understanding both its strengths and its limits is part of what makes it work well for the patients who pursue it. If you are trying to determine whether IV ketamine is the right fit for your specific history, a consultation is the most direct way to get a clear answer. Call us at 832-436-4055 or request a consultation online at sprashadmd.com — we will review your history honestly and tell you what we think your best options are.
References
- Antidepressant Efficacy in Treatment-Resistant Depression. PMC. https://pubmed.ncbi.nlm.nih.gov/23982301/
- Ketamine’s Effectiveness for Depression. Nature. https://www.nature.com/articles/s41398-021-01327-5
- NMDA Receptor / Glutamate System. PMC. https://pmc.ncbi.nlm.nih.gov/articles/PMC5148235/
- Ketamine Increases BDNF. PubMed. https://pubmed.ncbi.nlm.nih.gov/39684808/
Medical Disclaimer
The information in this blog is for educational purposes only and does not constitute medical advice. IV ketamine therapy should only be pursued under the supervision of a licensed psychiatric provider who is familiar with your full medical and psychiatric history. Individual results vary. If you are experiencing a mental health crisis or thoughts of self-harm, please call or text 988 to reach the Suicide and Crisis Lifeline or go to your nearest emergency room.