Ketamine’s duration depends entirely on what you mean by “working.” The anesthetic and dissociative effects of a single intravenous dose wear off in roughly five to ten minutes, while the antidepressant effects of that same dose can persist for up to a week. The route of administration, the dose, and the clinical goal all change the timeline dramatically. A person receiving ketamine for surgery, another using it for chronic pain, and a third getting infusions for depression are essentially on three different clocks.
How Long the Immediate Effects Last by Route
The way ketamine enters your body determines how fast it kicks in, how intense the peak feels, and how quickly the acute effects fade. Here is how the main routes compare:
- Intravenous (IV): Onset within 15 to 30 seconds. The primary anesthetic or dissociative effects last about 5 to 10 minutes, with residual effects lingering for 30 minutes to 2 hours afterward.1PubMed. Ketamine This is the fastest route and the one used in most clinical depression protocols, where the infusion itself typically runs for 40 minutes at a sub-anesthetic dose.
- Intramuscular (IM): Onset in about 3 to 5 minutes. Effects last roughly 12 to 30 minutes, with residual sedation or altered perception for up to 2 hours.
- Intranasal: Peak blood levels arrive within 20 to 40 minutes, and bioavailability sits around 50%.2PubMed Central. Esketamine Nasal Spray: Mechanism of Action, Clinical, and Translational Science The dissociative window is shorter and generally milder than IV, which is part of why the FDA-approved nasal spray (esketamine, marketed as Spravato) is administered in a clinic where you are monitored for about two hours.
- Sublingual: Detectable in the blood within 5 minutes, with peak levels at roughly 45 minutes. Bioavailability hovers around 24 to 32%.3PubMed Central. The absolute bioavailability of racemic ketamine from a novel sublingual formulation The lower bioavailability means a gentler ride, but the subjective effects can stretch out over an hour or more because of slower absorption.
- Oral: Bioavailability is similar to sublingual, roughly 23 to 24%.4Pain Medicine. Bioavailability of Ketamine After Oral or Sublingual Administration But a large fraction of the drug gets converted to norketamine during first-pass metabolism in the liver, and norketamine itself has pharmacological activity. So the “effect profile” of oral ketamine is different from IV, not just weaker. The combined contribution of ketamine plus norketamine actually brings the effective bioavailability up to around 54 to 59% for both oral and sublingual routes.4Pain Medicine. Bioavailability of Ketamine After Oral or Sublingual Administration
These timelines describe the acute, perceptible effects: the dissociation, the sedation, and the analgesia you can feel. They do not tell you how long ketamine is still active at a molecular level. Ketamine’s plasma half-life varies depending on how it is measured. One early study of IV infusions reported about 79 minutes, while another pharmacokinetic analysis found a terminal half-life of around 186 minutes when tracking the slower phase of elimination.5PubMed. Ketamine infusions: pharmacokinetics and clinical effects6Journal of Pharmaceutical Sciences. Bioavailability, Pharmacokinetics, and Analgesic Activity of Ketamine in Humans The discrepancy reflects the fact that ketamine distributes into tissues and then slowly washes back out, so the drug hangs around longer than the subjective effects suggest.
How Long Antidepressant Effects Last After a Single Dose
The reason ketamine has generated so much excitement in psychiatry is speed. A single sub-anesthetic IV infusion can produce a measurable drop in depression scores within hours, with the strongest effect typically appearing around 24 hours after the dose. A meta-analysis pooling data from randomized trials found that the largest antidepressant benefit over controls appeared at the 24-hour mark, and a significant difference persisted for up to 7 days.7PubMed Central. Efficacy of single and repeated administration of ketamine in unipolar and bipolar depression: a meta-analysis of randomized clinical trials That is extraordinary by psychiatric standards, where most antidepressants take weeks to show any effect at all.
But a week is also a ceiling for a single dose in most people. The mood benefits tend to fade gradually over the following days, and by two weeks the advantage over placebo is usually gone. This makes ketamine’s antidepressant effect fast but short-lived unless you keep dosing, which creates both a clinical opportunity and a practical problem.
Repeated Dosing and How That Changes the Timeline
Clinicians discovered early on that repeated infusions can build on each other. In a randomized controlled trial of patients with treatment-resistant depression, about 59% met response criteria after a series of infusions, with a median of three infusions needed before achieving response.8PubMed. Single, Repeated, and Maintenance Ketamine Infusions for Treatment-Resistant Depression: A Randomized Controlled Trial That same trial saw cumulative antidepressant effects and a doubling of the response rate compared to a single infusion. The same meta-analysis noted above found that at 2 to 3 weeks of repeated ketamine dosing, depression severity scores remained significantly lower than placebo.7PubMed Central. Efficacy of single and repeated administration of ketamine in unipolar and bipolar depression: a meta-analysis of randomized clinical trials
The question that follows is whether maintenance treatment can keep the effect going over months. A systematic review of maintenance ketamine treatment across IV, intranasal, oral, and other routes concluded that ongoing dosing does appear to sustain the antidepressant effect in treatment-resistant depression, though the quality of the evidence is still limited by study design.9PubMed. Maintenance ketamine treatment for depression: a systematic review of efficacy, safety, and tolerability In practice, many clinics taper patients to once-monthly or once-every-few-weeks infusions, but there is no universally agreed-upon schedule. The ideal spacing depends on how quickly symptoms return for each individual.
Duration of Anti-Suicidal Effects
One of ketamine’s most striking properties is its rapid effect on suicidal thinking, which conventional antidepressants barely touch in the short term. A meta-analysis pulling individual participant data from eight studies found that a single dose significantly reduced suicidal ideation as early as one day after infusion, with moderate-to-large effect sizes at every time point measured through one week.10PubMed Central. The effect of a single dose of intravenous ketamine on suicidal ideation: a systematic review and individual participant data meta-analysis Among those who had a resolution of suicidal ideation by 24 hours, roughly 86% in the ketamine group still had that benefit at one week, compared to about 53% in the control group.
A more recent meta-analysis reinforced these findings, showing ketamine was significantly more effective than placebo at reducing suicidal ideation on day one and that the benefit extended out to nearly a week.11Translational Psychiatry. A meta-analysis of the effects of ketamine on suicidal ideation in depression patients This makes ketamine one of the few pharmacological tools with a meaningful effect on acute suicidality in that first critical week, though it is not a long-term solution on its own.
Ketamine for PTSD and How Long Those Benefits Persist
Research on ketamine for post-traumatic stress disorder is newer and smaller than the depression literature, but the early results are intriguing. An initial randomized trial found that a single ketamine infusion significantly reduced PTSD symptom scores compared to an active placebo, with effects measurable at 24 hours and persisting through 72 hours.12JAMA Psychiatry. Efficacy of Intravenous Ketamine for Treatment of Chronic Posttraumatic Stress Disorder: A Randomized Clinical Trial
A subsequent trial of repeated infusions over two weeks in patients with chronic PTSD showed more durable results. Among those who responded to the treatment course, the median time to loss of response was about 27.5 days after the infusions ended.13PubMed. A Randomized Controlled Trial of Repeated Ketamine Administration for Chronic Posttraumatic Stress Disorder A systematic review and meta-analysis confirmed that ketamine produced statistically significant improvements in PTSD symptom scores, with the benefit becoming clearest by the end of a treatment course lasting one to four weeks.14PubMed Central. Effectiveness of Ketamine for the Treatment of Post-Traumatic Stress Disorder – A Systematic Review and Meta-Analysis So for PTSD, the timeline looks roughly similar to depression: rapid onset, a week or so of benefit from a single dose, and a few weeks of benefit from a course of repeated treatments.
How Long Side Effects Stick Around
If you are getting ketamine for the first time, one of the most practical questions is how long you will feel “off” afterward. The most common side effects are dissociation, dizziness, nausea, elevated blood pressure, blurred vision, and sedation. A detailed assessment of side effects from single IV ketamine infusions found that most peaked within the first hour and resolved completely by two hours.15PubMed Central. Comprehensive Assessment of Side Effects Associated with a Single Dose of Ketamine in Treatment-Resistant Depression The dissociative symptoms were the first to arrive and the first to leave. General physical symptoms like drowsiness and dizziness faded a bit more slowly but were essentially back to baseline by four hours.
A broader review of adverse effects across both ketamine and esketamine confirmed this pattern: the side effects are largely mild, transient, dose-dependent, and tend to lessen with subsequent treatments.16PubMed. Prevention and Management of Common Adverse Effects of Ketamine and Esketamine in Patients with Mood Disorders The reduction over repeated sessions is worth knowing about, because a rough first experience does not necessarily predict all future sessions.
Driving is a separate concern. A study that tested driving-simulator performance after analgesic-dose ketamine found significant impairment at the 2-hour mark, depending on what other medications were co-administered.17Journal of Clinical Psychopharmacology. Driving Simulator Performance After Administration of Analgesic Doses of Ketamine With Dexmedetomidine or Fentanyl Most clinics require patients not to drive for the rest of the day following an infusion, and that is a sensible precaution regardless of how “fine” you feel a few hours later. Cognitive effects can linger subtly even after the obvious dissociation has cleared.
Why Duration Varies So Much Between People
If you have read accounts of ketamine treatment, you have probably noticed that one person’s effects last days while another’s barely make it to 48 hours. Some of this is just biological noise, but two factors with real evidence behind them are genetics and age.
Ketamine is metabolized primarily by a liver enzyme called CYP2B6. A study of chronic pain patients found that people carrying two copies of a common genetic variant (CYP2B6*6) cleared ketamine from their blood at about a third of the rate of people without that variant.18British Journal of Clinical Pharmacology. CYP2B6*6 allele and age substantially reduce steady-state ketamine clearance in chronic pain patients: impact on adverse effects That variant combined with age explained about 60% of the variation in ketamine blood levels across patients. Higher blood levels from slower clearance mean a longer duration of both therapeutic and side effects, and potentially a higher risk of adverse reactions.
Age matters independently of genetics. Children metabolize ketamine faster than adults, so pediatric dosing is typically higher on a per-kilogram basis to achieve the same level of sedation or anesthesia. Older adults, on the other hand, tend to metabolize the drug more slowly, meaning effects last longer and doses generally need to be reduced to avoid excessive sedation.19PubMed Central. Optimizing ketamine dosing strategies across diverse clinical applications: a comprehensive review If you are in your 70s and being given the same dose as a 35-year-old, that is a conversation worth having with your provider.
The Role of Ketamine’s Metabolites
Part of what makes ketamine’s duration story complicated is that the drug itself is only half the picture. When your liver breaks down ketamine, it produces norketamine, and norketamine is further converted to hydroxynorketamine. Both of these metabolites are pharmacologically active, meaning they are doing things in the brain well after the parent drug has faded from your awareness.20PubMed Central. (R,S)-Ketamine metabolites (R,S)-norketamine and (2S,6S)-hydroxynorketamine increase the mammalian target of rapamycin (mTOR) function
This is especially relevant for oral and sublingual routes, where heavy first-pass metabolism means norketamine levels can actually exceed ketamine levels by a factor of two to five.21PubMed. Development of a sublingual/oral formulation of ketamine for use in neuropathic pain: Preliminary findings from a three-way randomized, crossover study In other words, if you take ketamine orally, you are getting a large dose of norketamine as a bonus. Whether norketamine contributes meaningfully to the antidepressant effect (as opposed to just the analgesic effect) is an active research question, but the pharmacological activity of these metabolites likely explains at least some of the gap between when the drug seems to wear off subjectively and when the therapeutic benefits actually fade.
Tolerance and What Happens With Long-Term Use
There is a tension at the heart of maintenance ketamine therapy: you need repeated doses to sustain the benefit, but repeated exposure can lead to tolerance. Animal research has shown that chronic ketamine administration produces dose-dependent tolerance to its anesthetic effects, meaning you need progressively more drug to achieve the same result.22PubMed Central. Ketamine Tolerance in Sprague-Dawley Rats after Chronic Administration of Ketamine, Morphine, or Cocaine
Human case reports reinforce this concern. One documented case involved a patient with major depression who self-administered ketamine intramuscularly over six months and gradually escalated from a therapeutic dose to daily injections of 2 grams, roughly three times an anesthetic dose, as tolerance to the antidepressant effect developed.23PubMed. Long-Term Ketamine Self-Injections in Major Depressive Disorder: Focus on Tolerance in Ketamine’s Antidepressant Response and the Development of Ketamine Addiction That is an extreme case involving unsupervised self-injection, but it illustrates the real risk of dose escalation when ketamine is used outside structured clinical protocols.
In supervised settings, tolerance development appears manageable for most patients, partly because treatment intervals are spaced out. The evidence on maintenance treatment suggests that antidepressant effects can be sustained with periodic dosing, though the optimal frequency and duration of maintenance therapy remain open questions.9PubMed. Maintenance ketamine treatment for depression: a systematic review of efficacy, safety, and tolerability Longer-term risks of repeated use, including bladder toxicity and cognitive effects, are less well characterized at the sub-anesthetic doses used for mood disorders than at the much higher doses seen in recreational use or chronic pain management.
Postoperative Pain and Procedural Sedation Timelines
Outside of psychiatry, ketamine is used heavily in surgical and emergency settings, and the duration expectations are different. For procedural sedation in emergency departments, a single IV push produces reliable dissociative anesthesia for five to ten minutes, which is enough time for a painful procedure like a fracture reduction or wound repair. The sub-anesthetic ketamine dose used for psychotic or dissociative effects in a research context is shorter still, with mental status changes lasting less than 30 minutes.24Neuropsychopharmacology. Subanesthetic doses of ketamine stimulate psychosis in schizophrenia
For postoperative pain, the approach is different. Rather than a single bolus, ketamine is often given as a low-dose infusion running alongside or after surgery, sometimes for up to 48 hours. A narrative review of its role in acute postoperative pain found that the most effective protocols combined a bolus dose around the time of surgery with a postoperative infusion, producing dose-dependent pain reduction over that window.25PubMed Central. Role of ketamine in acute postoperative pain management: a narrative review The pain-relieving effect of low-dose ketamine infusions in this context tends to last for the duration of the infusion and a few hours beyond, rather than persisting for days the way the antidepressant effect does.
This distinction is important because it underscores that ketamine’s various clinical effects operate on fundamentally different timescales. The direct blockade of pain signaling is tied closely to having the drug in your bloodstream. The antidepressant and anti-suicidal effects, by contrast, appear to depend on downstream changes in brain plasticity that outlast the drug’s presence by days. You can think of the acute effects as what ketamine does while it is there, and the psychiatric effects as what it sets in motion before it leaves.