Prescribing Ketamine and Esketamine

Why Ketamine Still Changes the Conversation

For seventy years, every antidepressant available worked the same way: nudge monoamines (serotonin, norepinephrine, dopamine) and wait four to six weeks to find out whether it helped. Ketamine broke that mold. It is the first antidepressant with a fundamentally different mechanism (glutamatergic, not monoaminergic) and, more strikingly, a fundamentally different tempo. A single dose can lift a severe depression within hours, and can cut suicidal ideation on day one, before ECT or TMS have even begun to work.

That speed is not a marketing gloss. In head-to-head terms, ketamine's antidepressant effect size runs 0.6 to 1.0, roughly two to three times that of a standard SSRI (~0.3). Around half of treatment-resistant patients show a meaningful response (≥50% symptom reduction) at 24 hours, versus under 10% on placebo. For a population defined by having already failed the conventional playbook, that is a remarkable number.

The catch, and the reason this guide is long, is that ketamine's benefit is fast but not durable. Single doses fade over days to weeks. Sustaining the response means repeated dosing, and repeated dosing raises questions the field has not fully answered: long-term safety, tolerance, abuse liability, and a genuinely unsettled post-discontinuation suicide signal. Layer on the REMS bureaucracy that governs esketamine (Spravato) and the two-hour in-office monitoring every dose requires, and you have a treatment that asks more logistical commitment than almost anything else in outpatient psychiatry.

A note on terminology, because it trips people up constantly:

• Ketamine is the racemic mixture: 50% S-ketamine (esketamine) plus 50% R-ketamine (arketamine). Used off-label, most commonly IV (0.5 mg/kg) or intranasal/compounded. Schedule III. Cheap. Not FDA-approved for depression.
• Esketamine (Spravato) is the purified S-enantiomer, delivered intranasally, FDA-approved for TRD and for depression with acute suicidality. It is governed by a REMS program, must be given in a certified center, and costs an order of magnitude more.

Counterintuitively, the FDA-approved, patented, expensive product is probably not the more effective one, more on that below. But it is the one insurers cover, and the one with the regulatory scaffolding built around it.

Part 1: Indications: Who Is Ketamine For?

FDA-Approved Uses (Esketamine / Spravato)

• Treatment-resistant depression (TRD) in adults, as an adjunct to an oral antidepressant. Approved March 2019.
• Depressive symptoms in adults with major depressive disorder and acute suicidal ideation or behavior (MDSI), again alongside an oral antidepressant. Approved 2020.

Note the structural feature: esketamine is approved added to an antidepressant, never as standalone monotherapy in the label.

The Evidence-Based Clinical Uses

Treatment-resistant depression: the home turf. This is where the evidence is strongest and where ketamine belongs in the algorithm. The working definition of TRD across most trials and clinical use is failure of at least two adequate antidepressant trials (adequate meaning roughly six weeks at a therapeutic dose). Response rates at four weeks in the esketamine registration trials ran about 53% (esketamine plus antidepressant) versus 37% (placebo plus antidepressant), an approximately 18-point drug-placebo separation, with remission around 22%. IV ketamine's numbers are frequently higher (40 to 70% response by 24 hours), and indirect meta-analytic comparisons favor IV racemic ketamine over intranasal esketamine.

Acute suicidal ideation: ketamine's signature speed. This is the setting where ketamine does something nothing else in the pharmacopeia does: it reduces suicidal ideation within hours. In hospitalized patients with active suicidality, esketamine 84 mg showed benefit for both depression and suicidal thoughts at 4 and 24 hours, faster than ECT or TMS can act. This makes it a genuine option for the acutely suicidal patient, potentially as an alternative to prolonged hospitalization when paired with close follow-up (intensive outpatient, partial hospital).

Bipolar depression: emerging, use with caution. Some trials show benefit, but the data are thinner and the risk of manic or mixed activation is real. If used, screen carefully for mixed and hypomanic features, monitor mood closely, and ensure adequate mood-stabilizer coverage.

Off-label and pilot-level indications. PTSD (dissociation may cut both ways: benefit versus traumatic recall), OCD, generalized and social anxiety: all have pilot data only. Reserve these for specialists.

Who Is the Ideal Candidate?

• Unipolar treatment-resistant depression (≥2 adequate failed trials): the strongest evidence.
• Acute suicidality where rapid action is critical and close follow-up is available.
• Severe depression where ECT is unavailable or declined, or that failed to respond to TMS (roughly half of TMS non-responders respond to ketamine).
• A patient with the temperament and life logistics to tolerate a dissociative experience and navigate a high-touch, supervised treatment.

Predictors of a Better Response

The literature is noisy here, but several signals recur:

• Family history of alcohol dependence (a fairly consistent early-response predictor)
• Prior suicide attempt (paradoxically, a positive prognostic sign)
• Comorbid anxiety
• History of childhood trauma has been reported as positive in some ketamine data, counterintuitive and not something to lean on clinically, but noted.

Who Is a Poor Candidate?

• Active substance use disorder (beyond nicotine) or high addiction risk: iatrogenic misuse risk.
• Active psychosis or psychotic-spectrum symptoms: ketamine is dissociative and PCP-like; it may worsen psychosis, and safety data are insufficient.
• Cardiovascular fragility: recent MI, uncontrolled hypertension, aneurysm or recent cerebral hemorrhage, significant coronary disease.
• Patients who cannot tolerate dissociation or the supervised model, or who lack the follow-through the treatment demands.

Part 2: Before You Start: Workup and Candidacy

The pre-start workup for ketamine is less about lab panels (this is not lithium) and more about cardiovascular screening, psychiatric and substance-use screening, and expectation-setting.

Baseline Assessment

Routine labs (CBC, CMP, LFTs) are not required for standard psychiatric-dose courses: hepatic and bladder toxicity are phenomena of chronic high-dose abuse, not supervised therapeutic dosing. Consider LFTs and urologic screening only if planning prolonged high-frequency maintenance.

Two Pre-Start Optimizations Worth Doing

Consider tapering benzodiazepines first. GABAergic drugs (benzodiazepines, Z-drugs) may blunt ketamine's glutamatergic mechanism and reduce efficacy. Where feasible, taper the benzodiazepine before starting, ideally with the last dose about 2 nights before the first ketamine dose. Reassuringly, one clinic found the benzodiazepine taper could be done concurrently with ketamine initiation without worsening depression, anxiety, or sleep: ketamine is powerful enough to cover the taper, making this a good deprescribing opportunity.

Set concrete behavioral goals. Ketamine works best embedded in a behavioral plan. Set two or three SMART goals ("out of bed and showered by 9 a.m. daily") so the rapid mood lift translates into changed behavior rather than evaporating.

Part 3: How to Start and Dose

There are three practical delivery routes. Match the route to coverage, access, and setting.

Oral Ketamine (Off-Label)

Bioavailability is low and erratic; dosing is unstandardized (ranges from roughly 1 mg/kg up to 50 to 300 mg). It carries the highest diversion risk of any route because it is home-dispensed. Not preferred for psychiatric use.

Route Selection at a Glance

Part 4: Monitoring: During, After, and Over Time

The Non-Negotiable Peri-Dose Monitoring

Every dose, every route:

• Blood pressure and heart rate: baseline before dosing, then during and after. Expect the systolic rise to peak around 40 minutes and settle within a few hours. Apply predetermined stopping criteria (Emory: SBP rise >45 mmHg, DBP rise >30 mmHg, or symptomatic severe hypertension: headache, chest pain, dyspnea, blurred vision).
• Sedation and dissociation: observe until resolved, typically 1–2 hours. For esketamine this ≥2-hour observation is REMS-mandated.
• No driving on treatment days. Arrange transport in advance.
• Suicidality: formal re-assessment after each dose and during maintenance.

Timing Landmarks Worth Knowing

• BP peak: ~40 minutes post-dose.
• Dissociation/sedation resolution: 1–2 hours.
• Maximum antidepressant effect: ~24 hours post-dose (well after the drug itself has cleared: half-life is only 2–4 hours). Don't judge efficacy in the dosing room; judge it the next day.

Longitudinal Monitoring

Part 5: Side Effects and How to Manage Them

The governing principle: the common side effects are acute, transient, expected, and self-limited. They resolve within 1 to 2 hours and are managed by preparation and observation, not by intervention. The serious long-term concerns are almost entirely phenomena of chronic high-dose abuse, not supervised therapeutic dosing. Keeping that distinction straight prevents most of the unwarranted fear around this drug.

Dissociation / Altered Perception (30–80%; >80% Report Something Strange)

The hallmark effect. Patients describe feeling "spacey," "floating," "woozy," "numb," "out of body." It tracks the drug's acute window and resolves in 1 to 2 hours.

Management:

• Prepare in advance: normalize it, frame it as temporary and expected, coach a "let go and be curious" stance rather than fighting it.
• Set the environment: dim room, blindfold, instrumental music (avoid lyrics with interpretable content); minimal interaction during the acute phase.
• Do not reflexively suppress it. Dissociative intensity may correlate with antidepressant response, so blunting it, especially with benzodiazepines, may reduce efficacy.
• A small fraction (1–5%) find the experience frightening enough to drop out; supportive presence and preparation minimize this.

Hypertension (the Most Reliable Physiologic Effect)

Mean systolic rise ~8–20 mmHg, peaking ~40 minutes, normalizing within hours. Roughly a third of patients experience a transient spike (>180/110). For perspective, that's less than a heavy exercise session or a panic attack produces.

Management:

• Baseline BP before each dose; monitor through the observation window.
• Predetermined stopping criteria (Emory thresholds, above): rarely triggered in practice.
• No routine antihypertensive is needed in most cases; the rise is self-limited.
• Extra caution in patients with cardiovascular risk; screen out the truly high-risk up front.

Nausea, Dizziness, Bitter Aftertaste (~5–10%)

Usually mild, transient, and tend to resolve as the dissociation abates.

Management: antiemetic PRN; the bitter aftertaste (intranasal) is brief and needs little beyond reassurance; often habituates over repeated doses.

Sedation (~10–20%)

Time-limited to the 1 to 2 hour window. Managed simply by the observation period and the no-driving rule; some patients prefer evening dosing.

The "Long-Term" Concerns: Keep Them in Proportion

These are the effects that generate the most anxiety and the most confusion, because the frightening data come almost entirely from chronic high-dose recreational abuse, not from supervised therapeutic use.

• Urinary/bladder toxicity (ketamine cystitis). About 25% of heavy recreational users report urinary symptoms; the mechanism is bladder cellular death and fibrosis. In supervised psychiatric use, it is extraordinarily rare: only a handful of documented cases across decades, and animal data show inflammation only at doses far above the clinical range. Ask about dysuria/hematuria on long maintenance; otherwise the risk is negligible.
• Hepatotoxicity. Seen with massive-dose, prolonged (40–50 hour) infusions and chronic abuse, not with standard psychiatric dosing. The FDA's LiverTox notes esketamine is not linked to biliary injury or cholestatic hepatitis under medical supervision.
• Cognitive impairment. Acute distortion lasts a few hours; there is no documented permanent impairment at clinical doses. Neuropsych testing at 6 weeks post-infusion shows no residual deficits. Cognitive problems appear only in heavy chronic abusers (grams per day, multiple days per week for years), and even those largely reverse with abstinence.
• Addiction/dependence. Case reports at therapeutic doses are a rarity (and mostly in atypical circumstances). No chemical dependence, no withdrawal syndrome; the risk is psychological and is managed by selection and supervision (see Parts 1 and 7).

Part 6: Overdose, Safety, and the Discontinuation Signal

There Is No Classic Overdose Toxidrome

Ketamine has a wide therapeutic index. Anesthetic doses (1–4.5 mg/kg IV) dwarf the psychiatric dose (0.5 mg/kg) and are used routinely in operating rooms; recreational users tolerate doses many times higher. This is a drug with far more margin than lithium: the acute danger is not "overdose" in the classic sense.

The Boxed Warnings

Racemic ketamine carries no boxed warning of its own; as a Schedule III controlled substance, it instead requires careful record-keeping and DEA compliance.

The Post-Discontinuation Suicide Signal: Take This Seriously

This is the one safety issue that deserves genuine caution rather than reassurance. In the esketamine registration data, there were 6 deaths, including 3 completed suicides occurring 4, 12, and 20 days after the last esketamine dose (following the open-label active-treatment phase). The FDA attributed these to underlying illness severity, and they did not reach statistical significance. But two features are unsettling: the frequency looked unusual compared with ECT/TMS trials in similar populations, and some patients had no documented suicidality immediately before.

The leading hypotheses are a withdrawal-like phenomenon, possibly opioid-mediated (recall that naltrexone blocks ketamine's antidepressant effect, implicating the opioid system), or glutamatergic rebound. A trial is underway examining whether buprenorphine can prevent these post-discontinuation events and extend ketamine's benefit.

Part 7: Drug Interactions

Ketamine is metabolized largely by CYP3A4, CYP2C9, and CYP2B6. In practice, standard psychiatric medications rarely cause clinically meaningful pharmacokinetic interactions, and there are no absolute contraindications with common psychotropics; esketamine was, after all, studied added to ongoing antidepressants. The interactions that matter are pharmacodynamic.

Benzodiazepines and Other GABA Agonists: the Efficacy Interaction

• Mechanism: GABA agonists (benzodiazepines, Z-drugs, barbiturates) may blunt ketamine's glutamatergic action.
• Consequence: reduced acute dissociative effect and possibly reduced antidepressant efficacy.
• Management: taper the benzodiazepine before (or concurrently with) ketamine initiation; last dose ideally about 2 nights before the first ketamine dose. This is both an efficacy move and a deprescribing opportunity.

Naltrexone: the Efficacy-Abolishing Interaction

• Mechanism: ketamine's antidepressant effect depends partly on the opioid system.
• Consequence: in a double-blind study, naltrexone completely abolished the antidepressant response (a 58% response rate fell to zero), while dissociation was unaffected.
• Management: do not co-administer naltrexone with ketamine given for depression. If a patient needs opioid-antagonist therapy, ketamine is essentially neutralized.

Sympathomimetics and Blood-Pressure-Raising Agents

Ketamine itself raises BP via sympathomimetic-like effects. Stimulants, other sympathomimetics, and even the additive load with the patient's own baseline hypertension can compound the transient rise. Coordinate monitoring in patients on antihypertensives, and be cautious stacking BP-raising agents.

CNS Depressants

Because sedation is an expected effect, layering additional CNS depressants (opioids, sedative-hypnotics, alcohol) adds to sedation and respiratory-depression risk, relevant especially in obstructive sleep apnea.

Agents That Are Not the Answer for Maintenance

Worth knowing what has been tried and failed to prolong ketamine's benefit: lithium, riluzole, lamotrigine, and d-cycloserine have all failed as continuation agents. (Lithium may also theoretically dampen ketamine's NMDA-related mechanism; anecdotal.) Only repeated dosing and, to some degree, structured psychotherapy sustain the response.

Part 8: Special Populations

Pregnancy

No controlled human data. Ketamine is teratogenic in high-dose animal studies, though obstetric anesthetic use suggests relative safety at clinical doses. Recommendation: avoid unless depression or suicidality is severe and the risk-benefit clearly favors treatment; consider deferring to after delivery.

Lactation

Ketamine enters breast milk; infant risk is unclear and data are insufficient. Likely avoid; discuss risk-benefit explicitly if considered.

Elderly (≥65)

The flexible-dose geriatric esketamine trial fell just short of statistical significance (p = 0.06); the efficacy signal is present but weaker than in younger adults. Older patients also carry higher baseline cardiovascular risk, so monitor BP closely and consider slower titration. No mandatory dose reduction, but clinical caution is warranted.

Renal Impairment

Ketamine is cleared hepatically, not renally, so no specific renal dose adjustment is defined. Likely safe; monitor for accumulation only with repeated dosing in severe renal failure.

Hepatic Impairment

Metabolized by hepatic CYP enzymes, so significant cirrhosis likely warrants caution and possible dose reduction. No toxicity reports in the psychiatric population at standard doses.

Children and Adolescents

Off-label; not FDA-approved for pediatric depression. Data are limited to case reports. Reserve for severe, refractory cases under specialist oversight.

Part 9: Discontinuation and Maintenance: Where the Real Difficulty Lives

Here is the central, hard truth about ketamine: the antidepressant effect is fast but not durable, and there is no reliable way to make it last except to keep dosing.

The Relapse Problem

After a completed acute course, relapse rates run 55 to 89% within 4 weeks without maintenance. Median time-to-relapse across studies ranges from about one week to several months. A single course is not a cure; it is an acute intervention whose gains must be actively held.

There Is No Chemical Withdrawal, But There Is a Discontinuation Signal

Ketamine produces no chemical dependence and no withdrawal syndrome in the classic sense. But as covered in Part 6, there is an unresolved post-discontinuation suicide signal (3 suicides 4 to 20 days after last dose in the trials). So while tremor or autonomic withdrawal won't appear, discontinuation is not pharmacologically inert, and it demands vigilance.

Maintenance: What Actually Works

• The only proven maintenance strategy is repeated dosing at intervals matched to the drug's duration. The standard esketamine taper widens gradually: twice weekly × 4 weeks → weekly × 4 weeks → every 1 to 2 weeks thereafter, individualized to the longest interval that holds remission.
• Failed maintenance add-ons: lithium, riluzole, lamotrigine, d-cycloserine, all tried, all failed to extend benefit.
• Psychotherapy helps. CBT is the one psychotherapy with controlled evidence for extending ketamine's benefit; the Montreal ketamine-assisted psychotherapy model (SMART goals, preparation, integration with ACT) is a promising framework. The clinical maxim: "Ketamine opens the door; therapy walks through it; the patient does the work."

A Reasonable Discontinuation Approach

By analogy to a standard depressive episode, a defensible practice is a roughly 6-month continuation after achieving response, followed by a carefully monitored discontinuation trial to see whether improvement is sustained. If relapse occurs, reinitiate and attempt periodic discontinuation trials over time. Because the post-discontinuation window is where the suicide signal lives, taper spacing gradually, keep the standard antidepressant and therapy in place, and monitor closely through the transition.

Part 10: Ketamine vs the Alternatives

Ketamine's value is best understood by where it sits relative to the other tools for severe/resistant depression.

In head-to-head comparisons with ECT over about 3 weeks, both produced similar 40 to 50% improvement; ECT's benefits may be more enduring, ketamine's satisfaction higher. Remission rates for ketamine and TMS are broadly comparable (~20 to 30% each; ECT exceeds both).

Racemic Ketamine vs Esketamine: the Counterintuitive Punchline

Esketamine (the S-enantiomer) has stronger NMDA antagonism, but NMDA antagonism is likely a secondary, not the primary, antidepressant mechanism, so the greater potency at that receptor doesn't translate into greater clinical benefit. A 24-trial meta-analysis actually favored IV racemic ketamine (roughly twice as likely to achieve response/remission), and animal data suggest the R-enantiomer (arketamine, in development) may be the more potent, longer-lasting, less-rewarding, less-neurotoxic component. Racemic ketamine also costs roughly 5 times less. So why is esketamine the FDA-approved, widely used product? Because racemic ketamine is generic and unpatentable (Janssen pursued esketamine specifically because the pure enantiomer could be patented) and because insurance covers esketamine, not racemic ketamine. Coverage, not clinical superiority, drives much of the prescribing.

Mechanism: The Short Version

Ketamine's mechanism is genuinely different from every monoamine antidepressant, and understanding it explains both the speed and the maintenance problem.

• NMDA receptor antagonism is the classic mechanism (ketamine blocks the receptor within the channel), but the field increasingly views this as secondary rather than the primary driver of the antidepressant effect. (Tellingly, other NMDA antagonists like memantine lack ketamine's antidepressant punch.)
• The likely primary mechanism is downstream: a glutamate surge driving preferential AMPA receptor activation, which triggers mTOR signaling, BDNF release, and rapid synaptogenesis, the strengthening of synaptic connections thought to underlie the fast antidepressant effect. The active metabolite hydroxynorketamine may drive much of this AMPA-mediated effect independent of NMDA blockade.
• An opioid contribution is real and important: naltrexone completely abolishes the antidepressant effect (while leaving dissociation intact), implicating the endogenous opioid system, possibly relevant to the post-discontinuation signal.
• Pharmacokinetics: elimination half-life is only 2 to 4 hours, yet the peak antidepressant effect is at ~24 hours and a single dose can last days to weeks. The therapeutic effect is thus a downstream neuroplastic cascade, not the drug sitting on a receptor, which is exactly why the benefit outlasts the drug, and why it eventually fades once the plasticity window closes.
• Enantiomers: racemic ketamine equals 50% S-ketamine (esketamine) plus 50% R-ketamine (arketamine). Esketamine has higher NMDA affinity; arketamine may (in animals) be the more potent and better-tolerated antidepressant. Racemic-ketamine findings cannot simply be extrapolated to esketamine alone.

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