What are the side effects of ketamine?

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Last updated: September 29, 2026 • View editorial policy

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Side Effects of Ketamine

Ketamine's most clinically significant side effects include emergence reactions (hallucinations, delirium, vivid dreams) occurring in 10-30% of adults, cardiovascular stimulation (increased heart rate, blood pressure, cardiac output), and potential for abuse/dependence with prolonged use. 1, 2

Cardiovascular Effects

Ketamine produces dose-dependent sympathetic nervous system stimulation leading to:

  • Increased heart rate
  • Elevated blood pressure
  • Increased cardiac output

This makes ketamine potentially dangerous and should be avoided in patients with ischemic heart disease, cerebrovascular disease, or hypertension 1. The cardiovascular stimulation is mediated through sympathetic activation and can be enhanced when co-administered with sympathomimetics or vasopressin 2.

Psychiatric and Neurological Effects

Emergence Reactions

The most notable psychiatric side effect is emergence reactions occurring in 10-30% of adults, manifested by 1, 3:

  • Floating sensations
  • Vivid dreams
  • Hallucinations
  • Delirium
  • Anxiety and dysphoria
  • Disorientation

Co-administration of midazolam with ketamine minimizes these emergence reactions 1, 3. This is a critical clinical strategy when using ketamine in adults.

Abuse Context Effects

When misused or abused, ketamine produces 2:

  • Anxiety and panic attacks
  • Flashbacks
  • Feelings of detachment and being "spaced out"
  • Memory and attention impairment with recurrent high-dose use
  • Insomnia

Respiratory Effects

Unlike benzodiazepine/narcotic regimens, ketamine does not significantly depress airway or cardiovascular reflexes 1, 3. However:

  • Respiratory depression and apnea can occur with rapid IV administration of high doses 2
  • Brief respiratory depression was observed even with doses 5-100 times greater than intended in pediatric cases 1
  • Laryngospasm and airway obstruction are possible 2

Gastrointestinal Effects

Common GI side effects include 2:

  • Nausea and vomiting (more prevalent at higher doses) 4
  • Anorexia
  • Increased upper airway secretions (can be attenuated with atropine or glycopyrrolate) 5

Hepatobiliary Effects

Hepatotoxicity is common after high-dose ketamine, is dose-dependent, and usually transient 4. The FDA label notes 2:

  • Hepatobiliary dysfunction
  • Biliary duct dilatation with or without biliary obstruction (reported with recurrent use including misuse/abuse)

Urological Effects

High-dose ketamine-induced uropathy is a significant concern, particularly with chronic use 4. Reported symptoms include 2:

  • Dysuria
  • Increased urinary frequency and urgency
  • Urge incontinence
  • Hematuria
  • Cystitis (including interstitial, ulcerative, erosive, and hemorrhagic variants)
  • Hydronephrosis and reduced bladder capacity

Ocular Effects

  • Diplopia
  • Nystagmus
  • Elevation in intraocular pressure 2

Abuse and Dependence

Ketamine is a Schedule III controlled substance 2. Key concerns:

Physical Dependence

  • Develops with prolonged use
  • Withdrawal symptoms after discontinuation of frequent (>weekly), large doses include: craving, fatigue, poor appetite, anxiety 2

Tolerance

  • Reported with prolonged use
  • Higher doses required to produce same effect 2

Pediatric Considerations

The FDA warns about potential neurotoxicity in pediatric patients 2:

  • Safety and effectiveness not established in children <16 years
  • Animal studies show neuronal and oligodendrocyte cell loss during rapid brain development
  • Window of vulnerability: third trimester through first several months of life, potentially extending to ~3 years
  • Associated with prolonged cognitive deficits in learning and memory in animal models
  • Clinical significance unknown, but providers must balance benefits vs. potential risks

Drug Interactions

Critical interactions to monitor 2:

  1. Theophylline/Aminophylline: May lower seizure threshold—consider alternative to ketamine
  2. Sympathomimetics/Vasopressin: Enhanced sympathomimetic effects—closely monitor vitals
  3. CNS Depressants (benzodiazepines, opioids, alcohol): Risk of profound sedation, respiratory depression, coma, death—closely monitor neurological status and respiratory parameters

Dose-Dependent Considerations

Recent evidence suggests 4, 6:

  • Many adverse effects are dose-dependent
  • Psychiatric symptoms, emesis, and hepatotoxicity increase with higher doses
  • However, one study found no dose-dependent relationship in patient-reported side effects between 80-240 mg daily oral doses 6

Safety Profile Context

When monitored appropriately in hospital settings, ketamine appears safe 4. The evidence shows:

  • In pediatric endoscopic sedation studies, only 1/128 patients (1%) experienced transient hypoxemia with ketamine/midazolam 1, 3
  • No serious adverse events in properly monitored settings
  • Most side effects are mild, transient, and attenuate with subsequent treatments 7

Common pitfall: Failure to co-administer benzodiazepines in adults to prevent emergence reactions. Always consider midazolam co-administration when using ketamine in adult patients 1, 3.

References

1
Guideline

aga institute review of endoscopic sedation.

Gastroenterology, 2007

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This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.