Ketamine Treatment for Depression: How It Works, the Forms Available, and What the Science Says

Depression silences millions of people. It strips away motivation, pleasure, and the capacity to envision a future — and for roughly one in three people with major depressive disorder (MDD), standard antidepressants never fully lift that weight. For this population, ketamine treatment for depression has emerged as one of the most significant advances in modern psychiatry: a fast-acting, neurologically distinct therapy with a growing body of rigorous clinical evidence behind it.

This guide covers how ketamine works at a biological level, the three main forms available, what peer-reviewed science says about each, and what patients and families should realistically expect from the process.

The Depression Crisis: Why a New Approach Was Needed

Depression is the world’s leading cause of disability. According to the World Health Organization (WHO), approximately 280 million people globally live with depression — around 5.7% of the world’s adult population, with women affected at nearly twice the rate of men. In the United States alone, an estimated 21 million adults experience at least one major depressive episode each year, representing roughly 8% of the adult population (NIMH).

For the majority, first-line treatment — selective serotonin reuptake inhibitors (SSRIs), serotonin-norepinephrine reuptake inhibitors (SNRIs), and related medications — provides meaningful relief. But approximately 30% of MDD patients do not respond adequately to these medications even after multiple trials at appropriate doses. This is classified as treatment-resistant depression (TRD), defined as an inadequate response to at least two antidepressant trials.

TRD carries an outsized burden:

• Nearly half of all depression-related healthcare costs are attributable to TRD patients (Johnson & Johnson / NIMH data, 2025)
• TRD patients experience substantially higher rates of hospitalization, disability, and suicidal ideation
• Most patients have tried four or five medications before receiving a specialized TRD diagnosis
• The World Health Organization’s 2025 World Mental Health report found that 91% of people globally with depression are unable to access care at all

It is precisely for this population — and the clinicians who care for them — that ketamine treatment has emerged as an evidence-backed, fast-acting alternative unlike anything that preceded it.

How Does Ketamine Help Depression? The Neuroscience

Ketamine has been used as a surgical anesthetic since the 1970s. Its antidepressant potential was discovered by accident: researchers and clinicians noticed that patients recovering from ketamine anesthesia frequently reported striking improvements in mood. That observation launched decades of research into the underlying mechanism.

The answer lies in a fundamentally different brain system than the one targeted by conventional antidepressants:

Standard antidepressants work on the monoamine system, targeting serotonin, norepinephrine, or dopamine. They typically require 4 to 8 weeks of daily dosing before producing meaningful clinical effects.

Ketamine is an NMDA (N-methyl-D-aspartate) receptor antagonist that works on the glutamate system — the brain’s primary excitatory communication network. By blocking NMDA receptors, it triggers a rapid downstream cascade that:

1. Stimulates the release of BDNF (brain-derived neurotrophic factor)
2. Activates AMPA receptors, promoting synaptogenesis
3. Encourages the rapid regrowth of synaptic connections that chronic depression has eroded
4. Opens what researchers describe as a neuroplasticity window — a period when the brain is actively restructuring and more receptive to positive change

Critically, this process begins within hours of a single dose — not weeks.

A study published in Science (Vanderbilt University, May 2025) found that enhancing intracellular ERK signaling downstream of ketamine can extend its antidepressant effects by augmenting synaptic plasticity — pointing toward future treatments that could sustain ketamine’s rapid benefits over longer periods.

A separate 2025 systematic review and meta-analysis of 21 studies (927 participants) confirmed that ketamine significantly and rapidly reduces suicidal ideation in high-risk individuals — and that its anti-suicidal effects appear to operate through mechanisms distinct from its general antidepressant action.

Key Clinical Facts and Figures

The research base for ketamine in depression has grown substantially over the past decade. The following data points are drawn from peer-reviewed literature and regulatory filings:

Global Depression Prevalence

• Approximately 280 million people
• Source: WHO, 2024

U.S. Adults with MDD Annually

• Approximately 21 million
• Source: NIMH / J&J NDA Filing, 2025

Treatment-Resistant Depression Rate

• Approximately 30% of MDD patients
• Source: NIMH; J&J, 2025

Ketamine Antidepressant Onset

• Antidepressant effects may emerge within hours in some patients
• Source: Multiple RCTs

Remission Rate After 3 IV Infusions

• Some IV ketamine studies have reported remission rates exceeding 50% after serial infusions
• Source: University of Michigan Medicine

Spravato Monotherapy Remission (4 Weeks)

• 22.5% vs 7.6% placebo
• Source: TRD4005 Trial; FDA, January 2025

IV Ketamine Bioavailability

• Approximately 100%
• Source: Pharmacokinetic literature

Nasal Esketamine Bioavailability

• Approximately 48–50%
• Source: Janssen prescribing information

Oral Ketamine Bioavailability

• 17–29%
• Source: Compounding pharmacology literature

Spravato Initial FDA Approval

• 2019 (with oral antidepressant)
• Source: FDA

Spravato Monotherapy Approval

• January 21, 2025
• Source: FDA / Johnson & Johnson

Global Patients Treated with Spravato

• More than 140,000
• Source: Johnson & Johnson, January 2025

Suicidal Ideation Reduction

• Rapid reductions in suicidal ideation have been observed in some studies within hours of treatment
• Source: Supported by multiple meta-analyses and randomized controlled trials

The Three Forms of Ketamine Treatment for Depression

Not all ketamine-based treatments are the same. There are three primary forms — intravenous (IV), intranasal, and oral — each with distinct pharmacology, regulatory status, evidence quality, and practical implications.

1. IV Ketamine Infusion (Racemic Ketamine)

Intravenous ketamine is the most widely studied form. Administered directly into a vein at a sub-anesthetic dose (typically 0.5 mg/kg over 40 minutes), racemic IV ketamine contains both the R- and S-enantiomers of the molecule and achieves ~100% bioavailability, meaning every milligram administered reaches systemic circulation.

Clinical profile:

• Setting: Hospital outpatient departments or specialist infusion clinics under continuous monitoring
• Typical course: 6 infusions over 2–3 weeks (induction), followed by maintenance every 2–8 weeks depending on response
• Onset: Antidepressant effects are often reported within 2–4 hours of the first infusion
• Regulatory status: Used off-label for depression — not FDA-approved for this indication in the United States
• Insurance: Generally not covered by insurance due to off-label status
• Evidence: Robust, including multiple randomised controlled trials, long-term observational data, and real-world studies

A 2024 study published in the Journal of Affective Disorders (University of Michigan Medicine’s Bio-K Study) found that after just three IV ketamine infusions over 11 days, 52% of participants with severe treatment-resistant depression achieved remission. An additional 15% showed a meaningful partial response. Half of those who had experienced frequent suicidal ideation before treatment reported significant improvement.

A 2025 head-to-head comparison led by Mass General Brigham researchers (153 patients) found that IV ketamine produced relatively earlier and greater initial symptom improvements compared to intranasal esketamine — though both treatments demonstrated significant clinical utility. Separately, a PubMed-indexed observational study found that while IV ketamine and intranasal esketamine showed similar long-term remission rates, IV ketamine required fewer treatment sessions to achieve remission.

Important clinical note: A double-blind randomized trial published in JAMA Psychiatry (2025, KARMA-Dep 2) found that in an inpatient setting — where patients were receiving serial ketamine infusions alongside standard psychiatric care — ketamine showed no meaningful advantage over the active control (midazolam). Clinicians are advised to account for the treatment setting when interpreting ketamine’s evidence base, as outpatient infusion clinic data consistently show stronger outcomes.

2. Nasal Esketamine — Spravato

Intranasal esketamine (brand name: Spravato) was developed by Janssen Pharmaceuticals and is the only ketamine-derived treatment with formal FDA approval for depression. Unlike IV racemic ketamine, Spravato contains only the S-enantiomer — the more pharmacologically potent form — and achieves approximately 48%-50% bioavailability by bypassing liver first-pass metabolism through absorption across the nasal mucosa.

Regulatory milestones:

• 2019: FDA approved Spravato for treatment-resistant depression in combination with an oral antidepressant
• January 21, 2025: FDA approved Spravato as the first-ever standalone monotherapy for TRD — meaning it no longer requires co-prescription with a daily oral antidepressant

This 2025 monotherapy approval followed a priority FDA review and was supported by data from the phase 4 TRD4005 randomized double-blind placebo-controlled trial (NCT04599855). In that trial, Spravato met its primary endpoint at day 28, with statistically significant improvements across all 10 items of the Montgomery-Åsberg Depression Rating Scale (MADRS) compared to placebo. Improvements in depressive symptoms were observed as early as 24 hours after the first dose.

Key clinical figures from the TRD4005 trial:

• Remission at week 4: 22.5% (Spravato) vs 7.6% (placebo)
• Effect sizes of 0.48 (56 mg dose) and 0.63 (84 mg dose) — considered modest to moderate
• Meaningful MADRS score reductions across both the 56 mg and 84 mg doses vs placebo (P < .001)

Clinical profile:

• Administration: Self-administered nasal spray at a certified healthcare facility, under direct supervision
• Dosing: 56 mg or 84 mg per session; twice weekly for 4 weeks (induction), then weekly or biweekly
• Monitoring: Patients must remain on-site for 2 hours post-dose under the FDA’s REMS (Risk Evaluation and Mitigation Strategy) program — due to risks of sedation, dissociation, and elevated blood pressure
• Insurance: Eligible for coverage under most major U.S. insurance plans with prior authorisation
• Evidence: Very strong — multiple Phase 3 RCTs across 24 countries; more than 140,000 patients are estimated to have received treatment globally as of the 2025 monotherapy approval

The monotherapy approval is clinically significant for patients who cannot tolerate or do not wish to take daily oral antidepressants, and for those who face pill burden or polypharmacy concerns.

3. Oral Ketamine

Oral ketamine for depression is the least standardised and least regulated of the three forms. Available only as a compounded preparation (not approved by the FDA in any oral form for psychiatric use), oral ketamine faces a significant pharmacological limitation: extensive first-pass metabolism in the liver reduces bioavailability to just 17–29%, compared to ~48% for nasal esketamine and ~100% for IV.

Clinical profile:

• Setting: Sometimes prescribed for home use, without the safety monitoring structure of IV or nasal forms
• Evidence base: More limited compared to IV and nasal esketamine; smaller studies, greater inconsistency in dosing and outcomes
• Regulatory note: The FDA has explicitly stated that compounded oral ketamine is not equivalent to FDA-approved forms of ketamine-derived therapy
• Risk profile: Less well-characterised; not endorsed as a preferred option in major psychiatric guidelines

That said, research into oral ketamine is ongoing. A 2025 meta-analysis and randomized controlled trial published in ScienceDirect found oral ketamine showing antidepressant efficacy, with a number needed to treat (NNT) of approximately 5 for response — noting that it may improve treatment accessibility in settings where IV infusion clinics are unavailable. However, the authors acknowledged that the absence of standardised dosing and the lower bioavailability remain significant obstacles to its clinical adoption.

Most psychiatrists and major guidelines currently recommend IV ketamine or FDA-approved Spravato over compounded oral preparations for patients with TRD, citing the substantially stronger evidence profiles and better-defined safety monitoring protocols for the former two.

Comparing IV Ketamine, Spravato, and Oral Ketamine

IV Ketamine

FDA Approval

• Off-label for depression

Bioavailability

• Approximately 100%

Onset of Effect

• 2–4 hours

Dosing Flexibility

• Highly customisable

Insurance Coverage

• Generally not covered

Evidence Quality

• Strong (multiple RCTs)

Supervised Setting

• Yes (infusion clinic)

Sessions to Remission

• Fewer (vs intranasal esketamine)

Nasal Esketamine (Spravato)

FDA Approval

• Approved (TRD + MDD/SI)

Bioavailability

• Approximately 48%

Onset of Effect

• As early as 24 hours

Dosing Flexibility

• Fixed (56 mg or 84 mg)

Insurance Coverage

• Usually covered (with prior authorization)

Evidence Quality

• Very strong (Phase 3 RCTs)

Supervised Setting

• Yes (certified REMS clinic)

Sessions to Remission

• More (vs IV ketamine)

Oral Ketamine

FDA Approval

• Compounded; not FDA-approved

Bioavailability

• 17–29%

Onset of Effect

• Slower, variable

Dosing Flexibility

• Variable, unstandardised

Insurance Coverage

• Not covered

Evidence Quality

• Limited (smaller studies)

Supervised Setting

• Often home use — no monitoring

Sessions to Remission

• Unknown / unstandardised

Ketamine for Depression and Anxiety: What the Research Shows

Depression and anxiety frequently co-occur. Research consistently shows that 50–60% of people with MDD also experience clinically meaningful anxiety, whether generalised anxiety, social anxiety, or anxiety embedded within a depressive episode. Conventional antidepressants often partially address one condition while leaving the other undertreated.

A 2025 meta-analysis published in European Psychiatry (multiple institutions including Harvard T.H. Chan School of Public Health) examined ketamine therapy across patients with “anxious depression” versus “non-anxious depression.” Both groups showed significant improvement on the MADRS depression scale, with no statistically significant difference in treatment response between the two groups — suggesting ketamine may retain antidepressant efficacy even in patients with prominent anxiety symptoms.

The neurobiological basis for this is coherent: Ketamine’s effects on glutamatergic signaling appear to influence neural circuits involved in fear processing and emotional regulation, including the amygdala — the brain’s primary fear and threat-processing centre, which is consistently hyperactivated in anxiety disorders. Some studies have reported rapid reductions in depressive rumination and negative thought patterns following ketamine administration.

It is important to note that Spravato is FDA-approved for treatment-resistant depression and for depressive symptoms in adults with major depressive disorder with acute suicidal ideation or behavior.

What Does a Treatment Session Actually Look Like?

Understanding the practical reality of a ketamine session helps patients prepare appropriately. Here is a step-by-step overview:

1. Psychiatric evaluation: A qualified psychiatrist reviews your diagnosis, treatment history, current medications, and general health to confirm candidacy and select the most appropriate form of treatment.

2. Pre-session preparation: You will typically be advised to fast for a few hours before the session, arrange transport home (patients should not drive after treatment), and discuss any medications that may interact with ketamine.

3. The treatment session: For IV ketamine, you recline in a clinical chair while medication infuses through an IV line over approximately 40–60 minutes. For Spravato, you self-administer the nasal spray at a certified clinic and remain for the mandatory 2-hour monitoring period.

4. During the session, Many patients experience mild dissociation — a floating or dream-like state — which is expected, transient, and considered part of the therapeutic mechanism by some researchers. Clinical staff are present throughout.

5. Post-session: Most patients rest for the remainder of the day. Mood improvements are commonly reported anywhere from a few hours to the following morning.

6. Maintenance phase After an induction period (typically 6 IV sessions or 8 Spravato sessions over 3–4 weeks), patients transition to maintenance treatments every 2–8 weeks, calibrated to their individual response.

Safety and Side Effects

Ketamine and esketamine are well-tolerated when administered under clinical supervision. The most frequently reported side effects are transient and typically resolve within 1–2 hours after the session ends:

• Dissociation or perceptual disturbance (most common during the session itself)
• Dizziness and nausea
• Elevated blood pressure (monitored throughout)
• Headache and fatigue
• Altered taste or nasal discomfort (specific to Spravato)

A 2024 systematic review of more than 1,000 patients found hepatic adverse events to be rare and predominantly mild. The SUSTAIN-3 long-term extension study of Spravato followed patients for up to 6.5 years and affirmed an acceptable long-term safety profile. A 2025 real-world study confirmed that side effects in monitored patient cohorts were mild and transient.

Because ketamine has dissociative properties and some potential for misuse, both IV ketamine infusions and Spravato are administered exclusively under clinical supervision in certified settings. This structure is fundamental — not incidental — to their safety profile.

Who Is a Good Candidate for Ketamine Treatment?

Ketamine-based treatments are not first-line therapies. They are specifically indicated for patients who have not achieved adequate improvement from at least two antidepressant trials at appropriate doses and durations. Potential candidates typically have:

• A confirmed major depressive disorder diagnosis
• An inadequate response to two or more antidepressants
• Severe symptoms significantly impairing daily function, relationships, or occupational performance
• Suicidal ideation requiring rapid clinical intervention
• Co-occurring anxiety alongside treatment-resistant depression
• The capacity to attend supervised, in-clinic sessions

Contraindications may include certain cardiovascular or cerebrovascular conditions, active or history of psychosis, poorly controlled hypertension, or a personal or family history of ketamine or substance misuse. A comprehensive psychiatric evaluation is always the essential first step before beginning any ketamine-based treatment.

Frequently Asked Questions

1.Is ketamine the same as Spravato? Not exactly. Spravato (esketamine) is derived from ketamine but contains only the S-enantiomer, while standard racemic IV ketamine contains both R and S molecular forms. Spravato is FDA-approved for TRD; IV racemic ketamine is used off-label for depression. Both target the glutamate/NMDA system.

2.How quickly does ketamine work for depression? Many patients report meaningful mood improvements within hours of their first session. This speed of onset fundamentally distinguishes ketamine from conventional antidepressants, which typically require 4–8 weeks to reach full therapeutic effect.

3.Is ketamine treatment covered by insurance? IV ketamine infusions are generally not covered because they are used off-label. Spravato, being FDA-approved, is covered through many major U.S. insurance plans, typically requiring prior authorization. Individual coverage varies; a treatment provider can assist with verification.

4.Can ketamine treat both depression and anxiety? A 2025 meta-analysis confirmed that ketamine produces a comparable antidepressant response regardless of whether anxiety is a major comorbid feature. Its use for primary anxiety disorders (as opposed to anxiety comorbid with TRD) remains off-label and requires careful clinical evaluation.

5.Is oral ketamine for depression effective? Oral ketamine has significantly lower bioavailability (17–29%) compared to IV or intranasal forms, and a considerably smaller evidence base. Ongoing research is examining its potential, particularly for settings where IV clinics are inaccessible. Most current guidelines recommend IV ketamine or FDA-approved Spravato as preferred options.

6.What is the difference between the 2019 and 2025 Spravato approvals? The 2019 approval required Spravato to be used alongside a daily oral antidepressant. The January 2025 FDA approval — following a Priority Review — allowed Spravato to be used as a standalone monotherapy, expanding options for patients who cannot tolerate or do not wish to take daily oral antidepressants.

Conclusion

For too long, treatment-resistant depression was treated as a clinical dead end. Ketamine-based therapies have fundamentally changed that picture — with rapid onset, a novel mechanism of action, and a growing body of rigorous clinical evidence.

Whether a patient is considering IV racemic ketamine through a specialist infusion clinic, FDA-approved Spravato nasal spray (now available as a standalone monotherapy as of January 2025), or researching the emerging evidence base for oral preparations, the common thread is this: ketamine therapy operates through a mechanism that works even when conventional antidepressants have failed.

The evidence is not without nuance — inpatient adjunctive trials have shown weaker effects, long-term data continues to accumulate, and access disparities remain real. But for patients with treatment-resistant depression, the clinical case for considering ketamine-based treatment is now well-established in psychiatric literature.

The first step is always a comprehensive consultation with a qualified psychiatrist who can review your treatment history and help determine which path forward is most appropriate for your specific clinical situation.

About the Author

Written by Amy Della Rocca, MSN, MPH, PMHNP-BC — Clinical Director, Marpa Minds

*Marpa Minds | Best Spravato® & Ketamine Therapy Clinic, White Plains, NY*